EXPERIMENTAL  GENERAL  SCIENCE 
CLUTE 


EXPERIMENTAL     . 
GENERAL  SCIENCE 


BY 

WILLARD  NELSON  CLUTE 

AUTHOR  OF  "LABORATORY  BOTANY  FOR  THE  HIGH  SCHOOL,"  "OUR 
FERNS  IN  THEIR  HAUNTS,"  "AGRONOMY,"  ETC. 


WITH  96  ILLUSTRATIONS 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO. 

1012  WALNUT  STREET 


COPYRIGHT,  1917,  BY  P.  BLAKISTON'S  SON  &  Co. 


A  ^ii'VJ ''•••'     ,; 


THE  MAPLE  PRESS  YORK  PA 


PREFACE 

Much  of  the  demand  for  courses  in  General  Science  in  the 
schools  is  no  doubt  due  to  the  ever  increasing  complexity  of 
the  more  formal  sciences  there  presented,  but  this  is  by  no 
means  the  chief  reason  for  the  introduction  of  such  a  course. 
A  large  number  of  those  who  enter  high  school  leave  before 
completing  the  regular  program  of  studies  and  thus  fail  to 
become  acquainted  with  the  special  sciences,  and  still  others 
elect  courses  which  include  only  a  minimum^of  these  studies. 

The  principal  claim  of  General  Science  to  a  place  in  the 
curriculum  is  that  it  will  introduce  such  students,  early  in 
their  school  life,  to  some  of  the  fundamental  principles  of 
science  which  are  very  essential  to  their  success  and  happi- 
ness in  life  and  which  they  would  otherwise  miss  almost 
entirely. 

That  General  Science  is  also  needed  as  an  introduction  to 
the  special  sciences  can  scarcely  be  questioned.  Enthusiastic 
teachers,  engrossed  in  their  own  subjects,  usually  overestimate 
the  amount  of  knowledge  their  pupils  can  bring  to  bear  on  the 
work  in  hand  and  unconsciously  plan  their  courses  on  lines 
that  are  often  beyond  the  ability  of  the  student.  The  texts 
in  science  designed  for  use  with  high  school  classes  are  also  fre- 
quently at  fault,  referring  to  such  subjects  as  osmosis,  change 
of  state,  capillarity,  diffusion,  the  molecular  structure  of  mat- 
ter, and  chemical  elements  and  reactions  as  if  they  were  cus- 
tomarily taught  in  the  lower  grades.  In  consequence,  the 
study  of  science  appears  so  forbidding  to  the  beginner  that 
none  but  the  more  venturesome  elect  it,  and  at  a  time  when  the 
world's  interest  in  scientific  things  was  never  greater,  we  are 
confronted  with  the  discouraging  fact  that  in  the  schoolroom 


VI  PREFACE 

interest  in  this  most  fascinating  field  of  knowledge  is  steadily 
decreasing. 

The  aims  of  a  text  in  General  Science,  therefore,  appear  to 
the  author  to  be  at  least  fourfold :  to  awaken  in  the  student  an 
interest  in,  and  love  for,  science;  to  provide  him  early  in  his 
studies  with  a  fund  of  useful  information  regarding  scientific 
matters;  to  fit  him  for  successfully  negotiating  such  courses  in 
the  special  sciences  as  he  may  later  elect;  and  last,  but  by  no 
means  least,  to  initiate  him  into  the  laboratory  method  of  solv- 
ing new  problems  and  thereby  to  develop  his  powers  of  observ- 
ation, reasoning  and  judgment.  An  experimental  course  in  the 
general  principles  underlying  all  science  seems  designed  to 
most  effectively  accomplish  these  ends,  provided  the  principles 
are  adhered  to  and  the  teaching  of  the  elementary  parts  of  the 
special  sciences  avoided. 

When  the  basic  principles  of  the  technical  sciences  are 
analyzed  they  are  found  to  be  almost  entirely  physical  and 
chemical  in  their  nature,  since  change  in  form,  position,  or 
composition  is  the  rule  in  all  earthly  things.  Astronomy, 
Geology,  and  Biology,  with  all  their  subsidiary  divisions  and 
ramifications,  are  merely  studies  in  the  application  of  these 
principles  to  special  phases  of  nature.  The  theme  of  this  book, 
therefore,  is  matter  as  it  is  affected  by  energy  in  its  manifold 
forms.  In  order  to  make  the  contents  of  the  course  intelligible 
to  the  beginning  student,  no  previous  knowledge  of  the  subject 
on  his  part  is  assumed,  and  the  experiments  and  references  are 
concerned  with  things  with  which  he  is  already  familiar  or  can 
examine  for  himself  without  special  effort.  In  selecting  these, 
however,  the  whole  field  of  science  has  been  laid  under  tribute 
but  with  no  attempt  to  classify  the  matter  into  the  usual  formal 
divisions;  indeed,  the  effort  has  been  to  avoid  this.  At  the 
same  time,  the  work  forms  a  connected  whole  by  the  adoption 
of  a  related  sequence  which  develops  naturally  and  which  is 
further  knit  together  by  numerous  cross-references.  The 


PREFACE  Vil 

practical  exercises  that  follow  each  chapter  touch  upon  phases 
of  the  subject  not  mentioned  in  the  text  and  are  therefore  an 
integral  part  of  the  work  and  not  a  mere  review  of  the  text.  If 
the  student  is  encouraged  to  work  out  these  exercises  for 
himself,  it  will  be  found  .to  advance  his  knowledge  much  more 
satisfactorily  than  mere  recitations  about  them. 

In  arranging  the  chapters  dealing  with  human  physiology  to 
follow  those  concerned  with  the  more  fundamental  principles  of 
all  science,  it  has  been  possible  to  considerably  reduce  the 
matter  devoted  to  this  subject  without  omitting  anything 
essential,  since  a  large  part  of  the  usual  high  school  course  in 
physiology  is  taken  up  with  discussions  of  the  physics  and 
chemistry  of  the  bodily  processes.  If,  however,  it  seems  de- 
sirable to  have  physiology  precede  the  more  general  matter, 
the  student  should  be  required  to  study  carefully  the  other 
sections  of  the  book  in  which  the  laws  underlying  physiological 
processes  are  treated  at  greater  length. 

The  matter  in  this  book  has  been  used  by  the  author  with 
his  classes  in  a  large  city  high  school  for  several  years,  and  the 
practicability  of  the  course,  and  especially  of  the  experiments, 
has  been  tested  under  a  variety  of  circumstances.  In  prepar- 
ing the  work  for  publication  the  author  has  had  the  advice  and 
assistance  of  several  of  his  fellow-teachers  to  whom  he  takes 
this  opportunity  of  acknowledging  his  grateful  appreciation. 
That  he  has  not  always  followed  the  advice  so  kindly  and 
cheerfully  given  will  account  for  any  errors  that  may  be  found 
in  the  text. 

WILLARD  N.  CLTJTE. 
JOLIET,   ILLINOIS. 


TO  THE  TEACHER 

This  book  is  so  arranged  that  it  may  be  used  exclusively  for 
recitations,  but  it  is  the  sincere  hope  of  the  author  that  it  may 
not  be  so  used.  In  no  subject  are  formal  recitations  less 
needed  than  in  General  Science.  All  the  pupil  needs  is  to  be 
helped  over  the  few  hard  places  which  happen  to  prove  too 
difficult  for  his  unaided  efforts.  In  this  way  may  be  developed 
the  initiative,  ingenuity,  and  originality  which  every  pupil 
possesses  in  greater  or  less  degree.  The  experiments  sug- 
gested are  such  as  may  be  performed  with  inexpensive  appa- 
ratus and  materials  and  have  been  selected  with  a  view  of  stim- 
ulating, as  far  as  may  be,  the  student's  interest  in  science. 
Except  in  the  very  few  instances  in  which  the  nature  of  the 
work  or  the  materials  makes  it  expedient  for  the  teacher  to 
perform  the  experiment,  it  will  doubtless  be  found  desirable  to 
require  each  student,  or  small  group  of  students,  to  do  the 
work  for  themselves.  In  general,  no  amount  of  observing  the 
work  of  others  can  take  the  place  of  individual  effort. 

The  ideal  way  of  handling  the  subject,  and  one  whose  worth 
has  been  proved  by  several  years  of  practice,  is  to  use  the  text 
as  so  much  explanatory  matter  to  be  drawn  upon  in  solving  the 
problems  presented  in  the  practical  exercises.  By  allowing 
each  pupil  to  work  for  himself,  the  brighter  students  are  not 
held  back  by  those  who  are  slower,  nor  are  the  latter  swept  off 
their  feet  in  trying  to  keep  up  with  the  class.  Pupils  who 
have  been  out  of  school  through  sickness  or  otherwise,  find 
upon  returning  to  such  a  class  that  they  are  at  no  disadvantage 
except  that  they  are  somewhat  less  advanced  in  the  subject 
and,  if  diligent,  may  soon  overtake  many  of  those  who  have 
not  been  absent.  Moreover,  much  of  the  work  may  be  per- 
formed at  home  if  desired.  If  the  extent  of  the  course  be 

ix 


X  TO    THE    TEACHER 

determined  in  advance,  with  the  amount  of  credit  to  be  given 
for  its  satisfactory  completion,  most  pupils  need  no  further 
stimulus  to  study. 

The  practicability  of  the  experiments  outlined  has  been 
demonstrated  repeatedly  by  classes  of  beginning  high  school 
pupils  working  for  themselves  in  an  ordinary  school-room 
equipped  only  with  water  and  gas.  A  shelf  should  be  provided 
for  the  few  articles  of  glassware,  reagents  and  other  chemi- 
cals needed,  and  each  student  should  be  required  to  return 
each  article  to  its  place  after  use.  The  questions  have  been 
numbered  to  facilitate  reference  to  them  and  the  work  may 
thus  be  abridged  or  expanded  at  any  point.  Throughout  the 
course,  the  best  results  will  be  secured  if  the  student  is  en- 
couraged to  investigate  each  subject  further  by  consulting 
dictionaries,  encyclopedias,  and  other  text-books,  and  by 
discussing  the  questions  with  classmates,  parents,  and 
teachers. 


CONTENTS 

PAGE 

PREFACE v 

To  THE  TEACHER ix 

CHAPTER  I.  THE  RELATIONSHIPS  OF  GENERAL  SCIENCE 

Scope — Scientific  methods — Special  sciences — Growth  of 
science — Practical  value — Practical  exercises. 

CHAPTER  II.  THE  UNIVERSE 

Extent — The  stars — Light  of  the  stars — Constellations 
— Motion  of  the  constellations — The  solar  system — The  sun 
— The  planets — The  moon — Eclipses — Shooting  stars  and 
comets — Time  on  the  earth — Practical  exercises. 

CHAPTER  III.  STRUCTURE  OF  MATTER 13 

Matter  and  energy — The  molecular  theory: — The  states  of 
matter — Some  properties  of  matter — Physical  and  chemical 
change — Practical  exercises. 

CHAPTER  IV.  ENERGY 18 

Movements  of  matter — Heat  and  molecular  motion — Forms  of 
energy — Kinetic  and  potential  energy — The  source  of  energy 
— Heat  and  light  compared — Practical  exercises. 

CHAPTER  V.  COMPOSITION  OF  MATTER 24 

Chemical  elements — Distribution  of  the  chemical  elements — 
Chemical  symbols  and  formulas — Chemical  compounds 
— Proportions  of  elements  in  compounds — Chemical  affinity 
— Heat  and  chemical  change — Practical  exercises. 

CHAPTER  VI.  THE  MEASUREMENT  OF  MATTER 33 

Standards — The  advantage  of  the  metric  system — The  meter 
— Divisions  of  the  metric  system — Grams  and  liters — Practical 
exercises. 

CHAPTER  VII.  DENSITY  AND  SPECIFIC  GRAVITY 39 

Weight — How  density  is  measured — Specific  gravity — Buoy- 
ancy— Practical  exercises. 

CHAPTER  VIII.  MEASUREMENT  OF  TEMPERATURE 46 

How  measured — The  thermometer — Graduating  the  ther- 
mometer— Absolute  zero — Changing  from  Fahrenheit  to  Centi- 
grade— Other  thermometers — Practical  exercises. 


Xll  CONTENTS 

CHAPTER  IX.  EFFECT  OF  HEAT  ON  VOLUME M 

Cohesion — Melting  point — Expansion  of  gases — Effects  of 
withdrawing  heat — Casting — Some  practical  applications 
— Practical  exercises. 

CHAPTER  X.  HEAT  AND  CHANGE  OP  STATE 60 

The  calorie — Specific  heat — Latent  heat — Practical  applica- 
tions— Practical  exercises. 

CHAPTER  XI.  PRESSURE  AND  CHANGE  OF  STATE 66 

Boiling  affected  by  pressure — Compression  of  gases — Heat  and 
compression — The  pressure  cooker — Refrigeration — Other 
uses  of  pressure — Practical  exercises. 

CHAPTER  XII.  COMBUSTION  AND  OXIDATION 72 

Activity  of  oxygen — Heat  and  light  from  oxidation — Kindling 
temperature — Products  of  combustion — Preparing  oxygen 
and  carbon  dioxide — Carbon  dioxide — The  Bunsen  burner. 
— Practical  exercises. 

CHAPTER  XIII.  CONDUCTION  AND  RADIATION 83 

Transference  of  heat — Conduction — Radiation — Insulators 
— Absorption  and  reflection — Distribution  of  heat — The  lag  in 
temperature — The  effects  of  gas  and  dust  on  radiation — Heat 
and  living  things — Uses  of  radiation  and  conduction — Practical 
exercises. 

CHAPTER  XIV.  CONVECTION 95 

Convection  currents — Winds — Convection  in  liquids — Con- 
vection and  frost — Practical  exercises. 

CHAPTER  XV.  EVAPORATION 101 

Conditions  affecting  evaporation — Boiling — Gases  and  vapors — 
Uses  of  evaporation — Practical  exercises. 

CHAPTER  XVI.  MOISTURE  IN  THE  AIR 106 

Variation  in  amount — Humidity — The  hygrometer — Forms  of 
condensation — Cloud  forms — Practical  exercises. 

CHAPTER  XVIi.  CAPILLARITY  AND  OSMOSIS 113 

Water  surfaces — Absorption  by  capillarity — Deliquescence — 
Shrinking  and  warping — Osmosis — Practical  exercises. 

CHAPTER  XVIII.  PRESSURE  OF  THE  AIR 119 

The  atmosphere — Weight  of  the  air — Function  of  the  air  con- 
stituents— The  barometer — Lift  pumps  and  siphons — Practical 
exercises. 

CHAPTER  XIX.  SOLUTIONS 129 

Solutes  and  solvents — Conditions  affecting  solution — Strength 
of  solutions — Crystallization — Mineral  waters — Hard  water — • 


CONTENTS  Xlll 

Diffusion — Other  forms  of  solutions — Alloys — Solution  and 
change  of  state — Emulsions — Practical  exercises. 

CHAPTER  XX.  PRECIPITATION,  FILTRATION  AND  DISTILLATION.  139 
Precipitates — Filters      and      filtering — Distillation — Practical 
exercises. 

CHAPTER  XXI.  ACIDS,  BASES  AND  SALTS 145 

Nature  of  Acids — Bases — Formation  of  salts — -Practical  exer- 
cises. 

CHAPTER  XXII.  LIGHT  AND  VISION 149 

Radiation  from  luminous  bodies — Reflection  of  light — Refrac- 
tion— -Lenses — The  camera — Persistence  of  images — -Various 
effects  of  light — Phosphorescence — 'Artificial  lighting — Prac- 
tical exercises. 

CHAPTER  XXIII.  COLOR 160 

Composition  of  light — Absorption  and  reflection — Fluorescence 
— Complimentary  colors— The  eye  and  color — Practical  exer- 
cises. 

CHAPTER  XXIV.  SOUND 167 

Vibrations  in  air — Echoes — Sympathetic  vibrations— Distin- 
guishing sounds — Practical  exercises. 

CHAPTER  XXV.  FORCE  AND  MOVING  BODIES '.    .   173 

Momentum  and  inertia — Friction — Advantages  of  friction — • 
Gravity — Equilibrium — Practical  exercises . 

CHAPTER  XXVI.  LONGITUDE  AND  TIME 181 

Locating  points  on  a  globe — Distances  on  the  earth — Time  on 
the  earth — Time  belts — The  earth's  axis  and  the  zones — Prac- 
tical exercises. 

CHAPTER  XXVII.  MACHINES 188 

Mechanical  advantage — Simple  machines — The  lever  and  its 
adaptations — The  inclined  plane  and  its  adaptations — The  hy- 
draulic press — Practical  exercises. 

CHAPTER  XXVIII.  MAGNETISM 194 

The  lodestone — Poles  of  the  magnet — The  earth  a  magnet — 
The  compass — Lines  of  force — Practical  exercises. 

CHAPTER  XXIX.  STATIC  ELECTRICITY 199 

Electricity  by  friction— Two  kinds  of  electricity — The  electro- 
scope— Insulators — -The  Ley  den  jar — Lightning — Practical  exer- 
cises. 

CHAPTER  XXX.  CURRENT  ELECTRICITY 205 

Useful  electricity — The  voltaic  cell — Direction  of  the  current — 


XIV  CONTENTS 

Induced  currents — Electroplating — Electromagnets — Electric 
light  and  heat — Storage  batteries — Practical  exercises. 

CHAPTER  XXXI.  LIVING  THINGS 211 

Organic  and  inorganic  bodies — Cells — Growth — Food  making 
— Digestion — Respiration — Reproduction — Species  and  higher 
groups — Scientific  names — Distribution — Plant  and  animal 
forms — Practical  exercises. 

CHAPTER  XXXII.  EVOLUTION 223 

Origin  of  living  things — Change  in  nature — Organic  evolution — 
Variation  in  nature — The  struggle  for  existence — The  Muta- 
tion Theory — Elementary  species — Plant  and  animal  breeding 
— Practical  exercise. 

CHAPTER  XXXIII.  BACTEKIA 231 

Nature  of  bacteria — Helpful  and  harmful  species — Toxins  and 
ptomaines — Antitoxins — Disinfectants  and  antiseptics — Prac- 
tical exercises. 

CHAPTER  XXXIV.  THE  FRAMEWORK  OF  THE  BODY 237 

The  skeleton — -Arrangement  of  the  skeleton — Joints — Muscles 
tendons,  and  ligaments — Value  of  exercise — Breaks,  sprains, 
and  deformities — Practical  exercises. 

CHAPTER  XXXV.  THE  GOVERNOR  OF  THE  BODY 245 

Need  of  a  governor — The  brain — The  spinal  cord — Involuntary 
action — Reflex  action — Pain  and  the  nerves — Sleep — Practical 
exercises. 

CHAPTER  XXVI.  THE  NOURISHMENT  OF  THE  BODY 250 

The  need  of  food — Value  of  foods — The  digestive  system — 
Structure  of  the  alimentary  canal— Digestive  juices — The 
teeth — Practical  exercises. 

CHAPTER  XXVII.  THE  TRANSPORTING  SYSTEM  OF  THE  BODY.    .  259 
The  blood — Absorption — Functions  of  the  blood — The  heart — 
Circulation  of  the  blood — Regulation  of  the  blood  stream — • 
Bleeding — Practical  exercises. 

CHAPTER  XXVIII.  THE  VENTILATING  SYSTEM  OF  THE  BODY.    .  268 
Respiration — Organs  of  breathing — Breathing — Ventilation — • 
The  voice — Colds — Expression  of  the  feelings — Practical  exer- 
cises. 

CHAPTER  XXXIX.  THE  COVERING  OF  THE  BODY 275 

The  skin — Structure  of  the  epidermis — The  dermis — Out- 
growths of  the  skin — Glands  of  the  skin — Functions  of  the  per- 
spiration— Care  of  the  skin — Practical  exercises. 


CONTENTS  XV 

CHAPTER  XL.  THE  EXCRETION  OF  WASTE  FROM  THE  BODY.    .    .  280 
Need  for  excretion — The  kidneys — Conditions  affecting  excre- 
tion— Practical  exercises. 

CHAPTER  XLI.  THE  SPECIAL  SENSES 284 

Function  of  sensations — The  special  senses — The  end  organs  of 
special  sense — Sight  and  hearing — Practical  exercises. 

CHAPTER  XLII.  THE  EFFECT  OF  DRUGS  ON  THE  BODY 291 

Drugs — Use  of  drugs — Tea,  coffee  and  other  beverages — To- 
bacco— Alcohol — Patent  medicines. 


EXPERIMENTAL  GENERAL  SCIENCE 

CHAPTER  I 
THE  RELATIONSHIPS  OF  GENERAL  SCIENCE 

1.  Scope. — When  one  begins  a  new  study  he  is  at  once  inter- 
ested in  discovering  what  ground  it  is  proposed  to  cover,  and 
what  methods  are  to  be  used  in  covering  it.     At  the  outset, 
then,  it  may  be  said  that  General  Science,  as  interpreted  in  this 
book,  is  concerned  with  the  general  principles  underlying  all 
manifestations  of  natural  phenomena,  together  with  a  study 
of  the  methods  which  man  has  devised  for  taking  advantage  of 
these  phenomena,  and  turning  them  to  his  own  account.     So  far 
as  we  know,  none  of  the  lower  animals  feel  an  interest  in  the 
laws  of  nature.     Man  alone  is  disposed  to  seek  the  causes  of 
things  and  to  add  to  his  store  of  knowledge  for  the  sheer  love 
of  learning. 

2.  Scientific  Methods. — The   word   Science,   itself,    comes 
from  the  Latin,  scientia,  meaning  to  know.     It  is,  in  fact,  exact 
knowledge  as  opposed  to  speculative,  second-hand,  and  hear- 
say information  which  may,  or  may  not,  be  true.     The  body 
of  scientific  knowledge  which  we  now  possess  has  been  estab- 
lished on  a  firm  basis  of  fact  by  multitudes  of  carefully  per- 
formed and  scrupulously  exact  experiments.     Many  of  these 
have  been  performed  time  and  again  by  different  observers 
in  order  to  set  at  rest  any  reasonable  doubt,  or  to  approach 
more  nearly  to  the  truth.     It  is,  of  course,  quite  possible  to 
gain  a  considerable  amount  of  scientific  knowledge  through  the 
reading  of  books,  but  such  methods  only  give  us  information 

1 


2  EXPERIMENTAL    GENERAL   SCIENCE 

regarding  things  already  known.  If  we  are  to  extend  the 
boundaries  of  our  knowledge,  we  must  strike  out  along  original 
lines,  and  study  things  themselves,  using  such  knowledge  as  we 
already  possess  to  aid  us  in  the  work.  The  laboratory  method, 
therefore,  is  highly  regarded  by  scientists,  and  may  well  be 
the  method  of  approach  by  even  the  beginning  student.  What 
one  finds  out  for  himself  by  observation  and  experiment  is 
understood  better  and  remembered  longer  than  information 
gained  in  any  other  way.  Besides,  one  cannot  really  be  said 
to  know  until  he  has  seen  and  experimented  for  himself. 

3.  Special  Sciences. — A  single  scientific  principle,  such  as 
the  fact  that  bodies  expand  on  heating  and  contract  on  cooling, 
or  that  the  air  has  weight,  has  hundreds  of  applications  in 
industry  and  in  the  arts.  When  such  principles  are  consid- 
ered in  their  relations  to  a  single  phase  of  nature,  they  may  give 
rise  to  special  sciences.  Among  the  special  sciences  are  astron- 
omy, which  treats  of  the  stars  and  other  heavenly  bodies; 
geology,  physiography  and  geography,  which  are  concerned  with 
the  structure  and  configuration  of  the  earth;  chemistry,  which 
deals  with  the  composition  of  all  things  and  the  changes  which 
they  undergo;  physics,  which  treats  specifically  of  the  changes 
in  form,  position,  and  temperature  of  different  substances;  and 
biology,  which  is  concerned  with  life  and  its  manifestations. 
The  latter  is  usually  divided  into  zoology,  which  treats  of 
animals,  and  botany,  which  deals  with  plants.  Physiology  is 
concerned  with  the  functions,  or  life  processes,  of  plants  and 
animals.  Arising  from  these  are  many  other  sciences,  such  as 
medicine,  pharmacy,  agriculture  and  engineering.  When  a 
science  is  studied  with  the  object  of  enlarging  the  boundaries 
of  our  knowledge,  it  is  usually  called  pure  science;  when  it  is 
studied  in  its  practical  or  useful  aspects,  it  is  called  applied 
science.  These  are  not,  however,  distinct  divisions.  The  dis- 
coveries of  workers  in  the  field  of  pure  science  are  often  of  the 
highest  value  in  practical  affairs,  while  were  it  not  for  the 


THE   RELATIONSHIPS   OF   GENERAL   SCIENCE  6 

practical  man,  the  scientist  would  lack  many  of  his  greatest 
conveniences. 

4.  Growth  of  Science. — The  knowledge  of  scientific  things 
was  the  latest  department  of  the  human  understanding  to  be 
developed.    Long  before  scientific  methods  came  to  be,  art, 
music,  literature,  history,  mathematics,  and  many  other  such 
subjects   of   study   flourished.     "The   scientific   attitude   of 
mind"  was  rare  in  the  days  before  the  tools  with  which  the 
scientist  now  works  were  invented.     When  the  microscope, 
the  telescope,  the  spectroscope  and  many  other  instruments  of 
precision  appeared,  scientists  made  rapid  progress.     In  the 
early  days,  too,  ignorance  and  superstition  conspired  to  retard 
scientific  progress,  and  even  sincere  and  inquiring  minds  found 
that  the  secrets  of  nature  were  discovered  with  difficulty.     In 
these  modern  days,  however,  the  conditions  are  changed,  and 
every  facility  is  offered  the  scientist  in  pursuing  his  investi- 
gations.    The  result  is  a  wonderful  development  of  all  phases 
of  science,  but  wonderful  as  the  advance  has  been,  it  is  prob- 
ably not  to  be  compared  with  what  the  future  has  in  store 
for  us.     A  general  knowledge  of  scientific  things,  therefore, 
has  become  almost  a  necessity. 

5.  Practical  Value. — The  practical  value  of  scientific  dis- 
coveries lies  in  the  power  it  gives  us  over  the  forces  of  nature,  to 
the  end  that  our  lives  may  be  made  easier,  happier,  and  richer. 
Few,  if  any,  of  our  modern  conveniences,  not  to  speak  of  lux- 
uries, would  be  possible  without  the  scientist.     Automobiles, 
telephones,  aeroplanes,  wireless  telegraphy,  submarines,  ther- 
mos bottles,  electric  lights,  steam  engines,  explosives,  and  a 
host  of  other  things  will  come  to  mind  in  this  connection.     The 
structure  or  operation  of  these  is  often  a  matter  of  special 
study,  but  one  does  not  need  to  be  a  machinist,  a  chemist,  or  a 
physicist  to  understand  the  principles  on  which  they  work. 
Moreover,  life  means  more  to  those  who  understand  why  it 
rains,  why  it  snows,  why  summer  is  hot  and  winter  cold,  why 


4  EXPERIMENTAL  GENERAL  SCIENCE 

warm  air  rises,  why  dew  forms,  why  grass  is  green,  and  the 
sky  blue.  To  solve  such  problems  by  the  study  of  nature's 
laws,  and  in  the  solving  to  train  the  mind  for  the  solution  of 
other  problems  that  may  come  up  in  later  life,  is  the  province 
of  general  science.  g 


CHAPTER  II 
THE  UNIVERSE 

6.  Extent. — Looking  up  at  the  sky,  especially  on  a  fine  night 
in  summer,  one  sees,  in  addition  to  the  many  brilliant  points 
which  we  call  stars,  a  broad,  faint  band  of  light  extending 
across  the  heavens  like  an  arch.     This  is  known  as  the  "  milky 
way."     When  it  is  examined  with  a  telescope,  it  is  found  to 
consist  of  a  great  many  bodies  like  our  own  sun,  though  most 
of  them  are  so  far  away  that  they  cannot  be  distinguished  by 
the  unaided  eye.     There  are  possibly  a  hundred  million  of  these 
suns  grouped  in  the  form  of  a  great  hoop  or  girdle.     The  reason 
why  we  do  not  see  this  great  assemblage  of  stars  or  suns  as  a 
circle  is  because  our  own  sun  is  located  within  it  and  well 
toward  the  center.     We  can  see  only  a  section  of  it  at  one  time, 
no  matter  from  what  part  of  the  earth  we  view  it,  but  if  the 
earth  were  moved  away  and  we  could  stand  in  its  place,  the 
circular  form  would  be  apparent.     So  far  as  we  know,  this 
great  ring  of  suns,  probably  many  of  them  with  attendant 
worlds  of  their  own  scattered  at  immense  and  inconceivable 
distances  from  one  another,  make  up  the  universe  in  which  we 
have  our  being. 

7.  The  Stars. — The  points  of  light  which  we  call  stars  are 
really  suns  like  those  of  the  milky  way;  in  fact,  they  may  be 
said  to  be  parts  of  the  milky  way,  the  only  difference  being 
that  those  we  call  stars  are  near  enough  to  us  to  appear  as 
separate  bodies  and  not  as  hazy  points  of  light.     Astronomers 
have  discovered  that  many  of  the  stars  are  larger  than  our  own 
sun — the  well-known  "dog  star,"  Sirius,  is  more  than  twenty- 
five  thousand  times  larger — and  appear  only  as  mere  points  of 
light  because  of  their  great  distances  from  us.     Our  own  sun. 

5 


6  EXPERIMENTAL   GENERAL   SCIENCE 

which  seems  so  brilliant,  is  probably  only  an  insignificant 
member  of  the  universe,  and  if  viewed  from  the  nearest  star, 
would  seem  like  a  mere  dot  in  the  sky,  if  it  could  be  distin- 
guished at  all.  The  difference  in  brightness  which  exists 
among  the  stars  affords  one  convenient  means  of  distinguishing 
them.  The  brightest  are  said  to  be  stars  of  the  first  magni- 
tude, the  next  brightest,  of  the  second  magnitude,  and  so  on  up 
to  the  sixteenth  magnitude.  There  are  less  than  twenty-five 
stars  of  the  first  magnitude.  All  the  more  conspicuous  stars 
have  names  of  their  own,  as  befits  their  importance;  others  are 
given  letters  with  reference  to  star  groups.  Some  of  these 
larger  stars  are  well  known  because  of  their  frequent  mention 
in  literature.  Among  these  are  Arcturus,  Aldeboran,  Polaris, 
Lyra,  Algol,  Rigel,  Capella  and  Vega. 

8.  Light  of  the  Stars. — All  the  visible  stars  are  hot  bodies 
like  our  sun,  and  shine  by  their  own  light.  There  is  some 
difference  in  the  quality  of  the  light,  as  may  easily  be  seen  by 
comparing  the  brighter  stars.  Some  have  a  bluish-white  light, 
while  others  incline  to  a  reddish  hue.  There  is  reason  for 
believing  that  this  difference  in  color  indicates  a  difference  in 
temperature,  and  that  the  blue  stars  are  much  hotter  than  the 
others.  There  are  also  large  numbers  of  suns  or  stars  that 
seem  to  have  cooled  off  so  much  that  they  no  longer  give  light, 
and  it  is  possible  that  these  dark  stars  greatly  outnumber  the 
bright  ones.  Our  own  sun,  like  the  others,  is  believed  to  be 
cooling  off,  and  in  time  may  cease  to  send  us  light  and  heat. 
This  event  is  so  far  distant,  however,  that  millions  of  years 
must  elapse  before  it  occurs.  The  light  that  comes  to  us  from 
the  stars  moves  at  the  rate  of  about  186,000  miles  a  second,  but 
even  at  that  speed,  the  time  required  for  the  light  of  some  stars 
to  reach  us  must  be  measured  in  hundreds  or  thousands  of 
years.  The  Pole  Star  (Polaris)  is  one  of  oifr  nearest  neighbors 
in  space,  but  it  requires  forty-five  years  for  a  ray  of  light  to 
travel  from  it  to  us. 


THE    UNIVERSE  7 

9.  Constellations. — From  the  earliest  times  the  stars  have 
been  favorite  objects  of  speculation  and  study,  and  much  was 
known  about  them  even  before  the  invention  of  the  telescope 
and  spectroscope  made  more  intimate  study  possible.     Long 
before  the  dawn  of  history,  man  had  looked  up  at  the  evening 
sky  and  fancying  the  stars  grouped  in  forms  resembling  earthly 
objects,  had  given  the  names  of  these  objects  to  the  groups. 
Such  groups  are  known  as  Constellations.     Among  the  more 
striking  of  these  are  the  Great  Bear,  the  Scorpion,  the  Northern 
Crown,  the  Southern  Cross,  the  Pleiades,  Sagittarius,  Orion, 
Booetes,  and  Pegasus.     Others  may  be  easily  distinguished 
on  a  clear  night.     The  seven  principal  stars  in  the  constella- 
tion of  the  Great  Bear  are  known  to  nearly  every  one  as  the 
"Big   Dipper."     The   constellations   are   not   really   related 
groups  of  stars,  although  they  appear  so  when  viewed  from  the 
earth.     All   are   moving  in  various   directions  through  the 
heavens,  and  in  time,  although  it  may  be  millions  of  years 
hence,  they  will  have  different  positions  from  those  they  now 
occupy. 

10.  Motion  of  the  Constellations. — Observers  of  the  heavens 
soon  discover  that  the  constellations,  though  retaining  their 
places  with  respect  to  one  another,  do  not  have  a  definite  posi- 
tion in  the  sky  but  steadily  drift  westward.     This  apparent 
motion  is  due  to  the  revolution  of  the  earth  about  the  sun 
which  thus  causes  us  to  view  them  from  a  different  position  in 
space  each  time  we  see  them.     They  are,  however,  to  be  found 
in  the  same  positions  on  the  same  dates  each  year  because  at 
the  end  of  a  year  we  have  returned  to  the  exact  spot  from 
which  we  viewed  them  a  year  earlier.     The  drifting  westward 
or,  rather,  our  change  in  position  with  regard  to  the  constella- 
tions, causes  one  after  another  to  disappear  in  the  west  while 
new  ones  appear  in  the  east.     For  a  part  of  each  year,  there- 
fore, some  of  the  constellations  are  invisible.     Among  those 
most  conspicuous  in  our  summer  skies  are  Booetes,  the  North- 


8  EXPERIMENTAL  GENERAL  SCIENCE 

era  Crown,  Sagittarius,  Pegasus,  and  the  Scorpion.  In 
winter  Orion  is  easily  the  most  conspicuous.  Owing  to  the 
rotation  of  the  earth  on  its  axis,  most  of  the  constellations 
appear  to  rise  and  set  nightly.  A  few  in  the  north,  including 
the  Great  Bear,  are  so  situated  with  respect  to  the  earth  that 
they  never  set  but  appear  to  circle  endlessly  about  the  pole 
star.  This  is  because  the  earth's  axis  points  toward  the  part  of 
the  heavens  in  which  the  pole  star — the  so-called  north  star — is 
located.  For  the  same  reason,  there  are  other  constellations 
that  never  rise  for  us,  being  below  our  southern  horizon  and 
hidden  from  us  by  the  great  bulk  of  the  earth.  Since  our 
north  pole  points  in  the  direction  of  the  north  or  pole  star,  an 
observer  at  the  pole  would  find  the  star  overhead,  and  at  the 
equator  it  would  be  on  the  horizon.  The  number  of  degrees 
the  pole  star  is  above  the  horizon  in  any  given  locality  is  the 
number  of  degrees  the  place  is  north  of  the  equator,  that  is,  it  is 
the  latitude  of  the  place. 

11.  The  Solar  System. — Our  sun  with  its  attendant  bodies, 
called  planets,  comprises  the  solar  system.     There  are  eight 
planets  which,  named  in  their  order  from  the  sun  outward 
through  space,  are  Mercury,  Venus,  Earth,  Mars,  Jupiter. 
Saturn,  Uranus,  and  Neptune.     As  seen  with  the  unaided  eye, 
most  of  the  planets  appear  as  rather  bright  stars.    Owing  to 
the   fact   that   they  '  are   so   near    us,  their  motion  is  very 
noticeable,  and  consequently  they  do  not  have  definite  places 
in  the  sky,  but  change  their  courses  with  the  seasons.     The 
ancients  called  such  stars  " planets"  (which  means  "wander- 
ers") to  distinguish  them  from  the  "fixed"  stars  which  seemed 
to  them  to  be  fixed  in  their  places.     Often  the  planets  are 
especially  noticeable,  as  when  they  appear  in  the  evening  sky 
shortly  after  sunset. 

12.  The  Sun. — Although  so  insignificant  compared  with  the 
other  stars,  our  sun  is  still  a  body  of  vast  dimensions.     It  is,  in 
fact,  about  a  million  times  larger  than  the  earth  and  seven 


THE    UNIVERSE  9 

hundred  and  forty  times  the  bulk  of  all  the  planets  combined. 
If  the  sun  were  represented  by  a  globe  twenty-five  feet  in 
diameter,  the  earth,  on  the  same  scale,  would  be  a  ball  three 
inches  in  diameter.  The  sun  is  the  source  of  light  and  heat  for 
the  planets,  and  the  center  about  which  they  all  revolve,  being 
held  in  their  courses  by  that  mysterious  force  called  gravity, 
which  acts  between  all  the  heavenly  bodies  with  a  strength  that 
is  in  proportion  to  their  masses  and  their  distances  from  one 
another. 

13.  The  Planets. — Of  the  eight  planets,  the  four  outermost 
are  larger  than  the  earth.     Jupiter,  the  giant  planet,  is  about 
fourteen  hundred  times  as  large.     The  average  distance  from 
the  earth  to  the  sun  is  92,800,000  miles.     Neptune,  the  farthest 
planet,  is  thirty  times  as  far,  or  nearly  three  billion  miles.     All 
the  planets  move  about  the  sun  from  east  to  west  in  periods  in 
proportion  to  their  distance  from  it.     Mercury  makes  a  com- 
plete revolution  in  eighty-eight  days,  while  Neptune  requires 
one  hundred  and  sixty-five  years  for  the  journey.     The  two 
planets  nearest  the  sun  have  no  moons  and  the  earth  has  only 
one,  but  Mars  has  two,  Jupiter  nine,  Saturn  ten,  Uranus 
four,  and  Neptune  one.     In  addition,  Saturn  has  a  broad  lumi- 
nous belt  of  rings  about  its  equator. 

14.  The  Moon. — The  earth's  only  satellite,  the  moon,  is  a 
much  smaller  body  which  revolves  about  it  just  as  the  earth 
itself  revolves  about  the  sun.     It  is  much  nearer  to  us  than 
the  sun,  being  in  fact,  only  two  hundred  and  forty  thousand 
miles  away.     It  makes  one  revolution  about  the  earth  in 
twenty-nine  days,  and  revolves  on  its  own  axis  once  during 
that  time,  in  consequence  of  which,  we  only  see  one  side  of 
it.     The  configuration  of  the  visible  side,  however,  is  as  well 
known  as  similar  areas  on  the  earth.     The  moon  shines  by 
reflected  sunlight,  but  the  amount  of  moonlight  we  receive 
varies  with  the  amount  of  the  illuminated  surface  visible. 
When  the  sun,  moon,  and  earth  are  in  such  a  position  that  we 


10  EXPERIMENTAL   GENERAL    SCIENCE 

see  the  fully  illuminated  half  of  the  moon,  we  call  it  full  moon. 
When  only  part  of  the  moon  is  visible  it  may  appear  as  a  cres- 
cent. The  new  moon  always  appears  in  the  western  sky  shortly 
after  sunset.  To  an  observer  on  the  moon,  the  earth  would 
appear  exactly  like  a  larger  and  brighter  moon.  The  fact  that 
the  earth  really  does  shine  to  the  other  planets  may  be  realized 
when,  as  occasionally  occurs,  the  whole  moon  is  faintly  outlined 
at  the  time  of  new  moon.  Since  the  bright  crescent  is  the 
only  part  that  reflects  the  sun's  rays,  the  faint  illumination  of 
the  rest  of  the  surface  must  be  due  to  earthshine.  This  appear- 
ance is  frequently  spoken  of  as  the  "old  moon  in  the  new 
moon's  arms." 

15.  Eclipses. — An    eclipse    always   occurs    when    a    body 
comes  between  any  of  the  heavenly  bodies  and  their  source  of 
light.     Eclipses  of  the  moon,  therefore,  are  caused  by  the 
earth  coming  between  the  moon  and  the  sun.     The  moon 
passes  into  the  earth's  shadow  and  is  totally  or  partially 
eclipsed.     Eclipses  of  the  sun  are  due  to  the  .passing  of  the 
earth  through  the  moon's  shadow;  that  is,  the  moon  passes 
between  us  and  the  sun,  cutting  off  the  sun's  light  from  us.     To 
an  observer  on  the  sun,  this  would  appear  as  an  eclipse  of  the 
earth.     The  reason  why  we  do  not  have  eclipses  of  the  moon 
more  frequently  is  because  its  path  about  the  earth  is  not  in  a 
plane  parallel  to  the  earth's  orbit  and  does  not  dip  into  the 
earth's  shadow  on  each  revolution. 

16.  Shooting  Stars  and  Comets. — On  a  clear  night,  we  may 
often  see  what  appears  to  be  a  star  falling  toward  the  earth. 
The  stars,  however,  do  not  fall.     What  seems  to  be  a  falling 
star  is  really  a  small  particle  of  matter  which  our  earth  has 
encountered  in  its  travels  through  space,  and  which  has  become 
so  hot  from  rubbing  against  our  atmosphere  that  it  shines. 
Such- bodies  are  often  called  shooting  stars,  or  meteorites.     They 
usually  consist  of  iron  or  stone.     Great  numbers  of  meteorites 
come  into  our  atmosphere  annually,  but  most  of  them  burn  up 


THE    UNIVERSE 


11 


before  they  reach  the  ground.  A  few  heavier  ones  have  fallen 
to  the  earth.  Some  of  these  weigh  more  than  a  ton  each. 
Specimens  may  be  seen  in  almost  any  large  museum.  Comets 
are  probably  aggregations  of  matter  similar  to  that  in  meteorites 
and  often  in  a  gaseous  form.  Some  comets  have  a  regular 
orbit  about  the  sun,  and  may  come  and  go  at  different  times. 
Others  may  appear  but  once  and,  traveling  past  the  solar  sys- 


Autumn 

FIG.  1. — Position  of  the  earth's  axis  with  reference  to  the  sun  during  the  year. 

tern,  finally  become  too  faint  to  be  seen  with  the  telescope,  and 
may  be  lost  among  the  distant  suns. 

17.  Time  on  the  Earth. — The  various  motions  of  the  earth 
serve  as  convenient  measures  of  time.  Thus  the  time  required 
for  the  earth  to  make  one  revolution  about  the  sun  is  a  year, 
while  its  rotation  on  its  axis  produces  day  and  night.  The 
month  is  partly  an  artificial  measure  of  time,  but  it  nearly  cor- 
responds to  a  revolution  of  the  moon  about  the  earth,  this 
latter  occurring  in  about  29  days.  The  movement  of  the  earth 


12  EXPERIMENTAL  GENERAL  SCIENCE 

about  the  sun,  in  connection  with  the  tilting  of  the  earth's  axis, 
causes  the  seasons  (§152).1  The  axis  is  so  directed  in  space 
that  first  one  pole  and  then  the  other  is  brought  nearer  to  the 
sun.  When  one  pole  is  toward  the  sun,  the  parts  of  the  earth 
near  it  have  summer  and  the  opposite  region  has  winter. 
Spring  and  autumn  are  the  seasons  between,  when  neither  pole 
is  nearer  the  sun.  It  is  the  inclination  of  the  earth's  axis, 
also,  that  causes  the  sun  to  be  higher  in  our  sky  in  summer  than 
in  winter.  The  sun  does  not  really  move  north  and  south  as 
the  seasons  change  but  only  appears  to  do  so  because  of  the 
apparent  change  in  the  earth's  axis. 

Practical  Exercises 

1.  Identify  as  many  constellations  as  you  can. 

2.  Locate  the  Pole  Star. 

3.  Examine  a  star  map  and  find  the  names  of  the  brighter  stars. 

4.  Find  out  from  the  almanac  where  the  planets  are  located  in  the 
sky  at  this  time  of  the  year,  and  identify  the  brighter  ones. 

5.  Make  a  drawing  showing  the  positions  of  the  axis  of  the  earth  with 
reference  to  the  sun  during  each  of  the  four  seasons. 

6.  Look  for  the  "earthshine"  at  the  next  new  moon. 

7.  The  moon  goes  around  the  earth  in  a  direction  the  reverse  of  the 
sun's  apparent  motion,  that  is,  from  west  to  east.    Can  you  account 
for  the  fact  that  the  moon  usually  rises  nearly  an  hour  later  each 
evening? 

8.  How  long  is  a  day  on  the  moon? 

1  The  references  are  to  other  sections  in  this  book  where  the  subject 
under  discussion  is  further  mentioned.  The  student  is  urged  to  consult 
all  such  references  as  an  aid  to  the  proper  understanding  of  the  subject. 


CHAPTER  III 
STRUCTURE  OF  MATTER 

18.  Matter  and  Energy. — It  makes  no  difference  whether  we 
consider  the  farthest  star  or  study  the  rocks  and  soil  of  which 
our  own  planet  is  composed,  we  everywhere  find  manifestations 
of  two  very  different  things  which  scientists  call  matter  and 
energy  respectively.     Matter  may  be  thought  of  as  anything 
that  occupies  space — animals,  plants,  air,  minerals,  water — in 
fact,  any  object,  big  or  little,  that  is  known  to  exist,  consists  of 
matter.     Energy,  on  the  other  hand,  is  the  power  to  do  work 
and  is  usually  seen  in  anything  that  moves  or  affects  matter, 
and  of  course  does  not  occupy  space.     Without  energy  the 
world  we  live  in  would  be  cold,  still  and  lifeless;  without  matter, 
it  could  not  exist  at  all.     Matter  and  energy  are  thus  sharply 
distinguished,  matter  being  a  substantial  thing,  while  energy  is 
that  which  produces  change  in  it.     Matter,  however,  is  not 
continuous;  that  is,  it  does  not  occupy  all  space.     Between 
the  earth,  with  its  enveloping  atmosphere,  and  other  heavenly 
bodies  are  vast  stretches  in  which,  so  far  as  we  know,  no  matter 
of  any  kind  exists.     Space  on  the  earth  that  does  not  contain 
matter  is  called  a  vacuum.     The  space  in  a  thermometer-tube 
above  the  mercury  is  a  nearly  perfect  vacuum. 

19.  The  Molecular  Theory. — All  matter  is  regarded  as  being 
made  up  of  very  small  particles,  called  molecules,  which  are  far 
too  small  to  be  seen  even  with  the  highest  powers  of  the  micro- 
scope.    Some  idea  of  how  small  molecules  really  are  may  be 
gained  from  the  fact  that  a  thimbleful  of  gas  at  ordinary 
temperatures  will  contain  more  than  75,000,000,000,000,000- 
000  molecules.     Although  nobody  has  ever  seen  molecules,  and 

13 


14  EXPERIMENTAL   GENERAL  SCIENCE 

probably  never  will,  scientists  have  devised  means  of  weighing 
and  otherwise  measuring  them,  and  thus  have  proved  the 
truth  of  what  has  long  been  known  as  the  molecular  theory  of 
matter. 

The  molecular  theory  enables  us  to  understand  how  it  is 
possible  for  matter  to  change  its  form.  Water,  for  instance, 
may  exist  as  a  solid  (ice),  a  liquid  (water),  or  a  gas  (steam),  and 
in  each  of  these  states,  the  same  quantity  has  a  different  size. 
If  matter  were  continuous  and  not  composed  of  many  small 
particles,  it  is  difficult  to  see  how  it  could  expand  and  contract 
in  this  way.  Various  experiments  may  be  performed  to  illus- 
trate the  molecular  structure  of  matter;  thus,  if  salt  is  slowly 
sifted  into  a  test-tube  of  water,  fine  bubbles  of  air  are  seen  to 
rise  to  the  surface.  These  air  bubbles  are  composed  of  mole- 
cules of  air  which  were  crowded  out  from  between  the  mole- 
cules of  water  by  the  salt.  Again,  water  at  high  pressure  may 
be  forced  through  sheets  of  solid  steel  or  other  metals,  and  car- 
bon dioxide  gas  easily  passes  through  red-hot  iron.  A  single 
drop  of  soapy  water  contains  so  many  molecules  that  when 
blown  into  a  soap  bubble  more  than  a  foot  in  diameter,  there 
are  enough  to  form  a  continuous  film  throughout. 

20.  States  of  Matter . — Water  is  not  the  only  substance  that 
may  exist  in  three  states — solid,  liquid,  and  gaseous.  Many 
other  substances  change  in  the  same  way  when  conditions  are 
favorable.  Each  state  has  certain  characteristics  peculiar  to 
it.  Solids  always  have  a  shape  of  their  own  and  resist  with 
considerable  force  any  effort  to  change  it.  When  solids  are 
changed  to  liquids,  however,  they  invariably  take  the  shape  of 
any  vessel  in  which  they  happen  to  be,  with  the  upper,  free, 
surface  level.  Gases  have  neither  shape  nor  size  (volume)  of 
their  own.  They  fill  any  space  open  to  them,  and  push  out- 
ward with  equal  force  in  all  directions.  For  this  reason,  they 
cannot  be  kept  in  an  open  vessel  like  solids  and  liquids.  If 
left  uncovered,  the  molecules  at  once  begin  to  fly  away.  If 


STRUCTURE    OF   MATTER  15 

the  space  containing  the  gas  is  made  larger,  the  gas  at  once  fills 
it,  and  if  it  is  made  smaller,  the  molecules  are  simply  forced 
closer  together.  In  some  cases,  if  the  gas  is  compressed 
enough,  the  substance  may  be  made  to  assume  the  liquid  form 
again.  The  fact  that  the  free  surface  of  a  liquid  is  absolutely 
level  is  often  taken  advantage  of  in  grading  and  building.  A 
hose  filled  with  water  may  be  used.  The  water  in  one  end  of 
the  hose  will  always  be  exactly  level  with  that  in  the  other 
(§98). 

21.  Some  Properties  of  Matter. — There  are  a  number  of 
properties  which  we  recognize  at  once  as  characteristic  of 
matter.  Among  these  are  weight,  hardness  and  brittleness. 
Other  characteristics  with  which  we  may  not  be  so  familiar 
are  elasticity,  tenacity,  malleability  and  ductility.  Elasticity  is 
the  tendency  of  matter  to  return  to  its  original  shape  and 
volume  after  being  bent,  compressed,  stretched,  or  twisted. 
Rubber  is  a  very  elastic  kind  of  matter,  and  air  is  another. 
Air,  it  is  true,  cannot  be  bent  or  twisted,  but  when  enclosed 
in  an  air-chamber  or  automobile  tire,  it  has  almost  perfect 
elasticity.  Tenacity  is  the  capability  of  a  thing  to  resist  being 
pulled  apart.  A  steel  wire  has  great  tenacity.  Malleability 
is  the  quality  of  withstanding  being  hammered  out  into  sheets 
without  cracking  and  ductility  is  the  capacity  of  being  drawn 
into  wire.  Copper  is  both  malleable  and  ductile;  limestone 
is  neither.  The  metal  platinum  is  so  ductile  that  it  may  be 
drawn  into  a  wire  scarcely  visible  to  the  eye.  Gold  may  be 
beaten  out  into  sheets  so  thin  that  it  would  require  300,000 
of  them  to  make  a  pile  an  inch  high.  Not  all  of  the  character- 
istics mentioned  are  likely  to  belong  to  any  one  substance, 
or  kind  of  matter,  but  all  substances  possess  several  of  them. 
There  are  many  other  qualities  that  characterize  different 
substances.  Some,  for  instance,  may  be  crystalline,  or  com- 
posed of  crystals;  others  may  be  without  definite  form,  or 
amorphous.  Glass,  pitch,  paraffin  and  similar  substances  are 


16  EXPERIMENTAL  GENERAL  SCIENCE 

amorphous.  Some  are  transparent  and  allow  light  to  pass 
through  them;  others  are  opaque  and  stop  the  light.  All  kinds 
of  matter  are  said  to  be  impenetrable  in  that  they  take  up  a 
certain  amount  of  space  to  the  exclusion  of  everything  else, 
and  they  are  also  indestructible — that  is,  they  cannot  be 
destroyed.  It  is  true  that  we  may  appear  to  destroy  matter, 
as  when  we  burn  a  block  of  wood  or  explode  gunpowder,  but  no 
matter  is  really  destroyed.  In  the  instances  mentioned,  mat- 
ter has  merely  changed  its  composition  and  now  exists  as  gas  or 
ashes,  or  both. 

22.  Physical  and  Chemical  Change. — The  changes  which 
occur  in  matter  may  affect  either  its  form  or  its  composition. 
When  the  change  does  not  affect  the  composition  of  matter,  as 
when  iron  is  melted  or  water  is  turned  to  steam,  it  is  called  a 
physical  change.  The  science  that  deals  with  such  changes  is 
called  physics.  When  the  composition  of  matter  is  changed, 
as  when  wood  burns,  iron  rusts,  or  quicklime  slacks,  it  is  called 
a  chemical  change.  Such  changes  are  studied  in  chemistry.  In 
physical  changes  the  original  substance  may  usually  be  recov- 
ered again  by  reversing  the  process  by  which  it  was  changed. 
Thus,  if  ice  be  heated  until  it  becomes  water,  it  may  be  turned 
to  ice  again  by  withdrawing  the  heat.  In  chemical  changes, 
one  or  more  new  substances  are  formed  and  the  original  sub- 
stance is  not  usually  to  be  obtained  again  by  reversing  the 
process.  Wood  once  burned  cannot  be  had  as  wood  again 
until  the  plant  has  built  it  up  once  more  from  the  gases  and 
ashes  into  which  it  was  turned  by  burning. 

Practical  Exercises 

1.  Why  does  one  have  difficulty  in  pouring  a  liquid  into  a  bottle 
through  a  close-fitting  funnel? 

2.  Dissolve  a  single  crystal  of  potassium  permanganate  in  a  test-tube 
of  water.     What  gives  the  color  to  the  water? 


STRUCTURE   OF  MATTER  17 

3.  How  much  water  will  a  crystal  of  potassium  permanganate  color? 


4.  What  does  the  foregoing  teach  as  to  the  size  and  number  of  molecules 
in  the  substance  used? 


5.  Select  the  substances  in  the  following  list  that  are  elastic,  those 
that  are  malleable,  and  those  that  are  ductile;  make  a  list  of  each:  iron, 
rubber,  clay,  lead,  glass,  coal,  ice,  copper,  wood,  limestone. 

6.  Name  the  solids,  liquids,  and  gases  in  the  following  list:  sand, 
mercury,  salt,  soda,  olive  oil,  steam,  air,  and  vinegar. 


7.  Arrange  the  following  in  two  lists,  one  of  physical  changes  and  the 
other  of  chemical  changes:  the  souring  of  milk,  the  melting  of  ice,  the 
rusting  of  iron,  the  rotting  of  wood,  exploding  gunpowder,  photographing, 
breathing,  evaporation. 


8.  Into  a  long  narrow  test-tube  half  full  of  water  pour  an  equal  amount 
of  alcohol.  Mark  the  exact  height  of  the  liquids,  cork  and  shake  well. 
How  do  you  account  for  the^difference  in  the  height  of  the  liquids  which 
you  can  now  observe? 


CHAPTER  IV 
ENERGY 

23.  Movements  of  Matter. — Matter  is  seldom,  if  ever,  in  a 
complete  state  of  rest.     Suns  and  planets  are  ever  in  motion 
through  the  heavens,  wind  blows,  smoke  rises,  water  evapor- 
ates, rain  falls,  and  grass  grows.     Even  when  the  substance 
does  not  move  as  a  whole,  its  molecules  are  in  rapid  motion.     A 
rock  or  a  piece  of  metal  expands  when  heated  and  contracts 
when  cooled,  thus  changing  both  its  size  and  temperature. 
Matter,  however,  cannot  move  of  itself.     All  the  movements 
which  the  various  forms  of  matter  exhibit  are  due  to  the  effects 
of  energy  upon  them. 

24.  Heat  and  Molecular  Motion. — All  of  the  molecules  of  a 
substance,  as  we  have  already  learned,  are  supposed  to  be  in 
constant  and  rapid  motion.     The  speed  of  a  molecule  of 
hydrogen  gas  at  ordinary  temperature  is  more  than  a  mile  a 
second.     Oxygen  molecules  travel  about  one-fourth  as  fast,  and 
the  molecules  of  other  substances  have  similar  speeds.     If  the 
molecules  of  the  air  moved  continuously  in  one  direction, 
instead  of  vibrating  back  and  forth,  it  would  produce  a  breeze 
of  more  than  fifteen  miles  a  minute,  a  velocity  sufficient  to 
blow  away  everything  in  its  path.     While  we  cannot  follow 
the  molecules  in  their  flight,  we  may,  by  proper  experiments, 
see  the  results  of  such  motion.     If  a  small  quantity  of  india-ink 
be  mixed  with  water  and  viewed  with  a  microscope,  each  par- 
ticle is  seen  to  be  in  rapid  oscillation.     Since  these  particles 
cannot  move  of  themselves,  their  motion  is  regarded  as  being 
caused  by  the  multitudes  of  molecules  colliding  with  them. 
The  motion  of  the  molecules  is  caused  by  the  heat  they  contain ; 

18 


ENERGY  19 

in  fact,  in  this  sense,  it  may  be  said  that  heat  is  motion,  for  by 
simply  increasing  the  heat  of  a  substance,  its  molecules  may  be 
made  to  move  faster  and  farther  apart,  while  withdrawing  the 
heat  reverses  the  action.  The  differences  noted  in  the  three 
states  in  which  matter  is  capable  of  existing  are  largely  due  to 
the  different  amounts  of  heat  they  contain,  for  solids  may  be 
made  liquid  by  adding  heat,  and  liquids  may  be  turned  to  gases 
by  adding  still  more  heat.  Adding  heat  to  a  gas  increases  the 
speed  of  its  molecules  and  causes  them  to  move  outward  with 
greater  force.  It  is  these  myriads  of  flying  molecules,  striking 
against  whatever  confines  them,  that  produces  the  pressure 
noted  in  all  gases  when  confined.  In  steam  boilers,  the  pres- 
sure of  the  confined  steam  sometimes  becomes  so  great  that  it 
causes  disastrous  explosions.  When  a  gun  is  fired,  it  is  the 
pressure  of  the  gas  generated  that  gives  the  speed  to  the  bullet 
(§53).  Gases  and  liquids  are  often  called  fluids.  The  mole- 
cules of  fluids  move  easily  and  smoothly  past  one  another,  but 
in  solids  the  motion  is  more  restricted.  All  are  in  motion, 
however. 

25.  Forms  of  Energy. — Besides  heat  and  the  energy  of 
motion  already  mentioned,  there  are  three  other  forms  of 
energy  that  are  more  or  less  familiar.  These  are  light  energy, 
electric  energy  and  chemical  energy.  All  forms  of  energy  are 
closely  related;  in  fact,  are  but  different  forms  of  the  same 
thing,  as  is  shown  by  their  changing  from  one  form  to  another, 
and  by  their  producing  changes  in  matter.  Electricity,  for 
instance,  may  be  produced  by  chemical  energy  and  used  to 
give  motion  to  cars,  elevators  and  the  like.  The  same  force, 
properly  treated,  will  light  the  cars,  and  if  desired,  heat  them 
as  well.  Chemical  energy  is  often  liberated  when  two  sub- 
stances are  united,  and  frequently  appears  in  the  form  of 
heat.  Water  put  on  quicklime  may  release  enough  chemical 
energy  to  boil  the  water.  Instances  of  this  are  often  seen 
when  plaster  is  being  mixed.  Sulphuric  acid  poured  into  water 


20 


EXPERIMENTAL   GENERAL   SCIENCE 


also  produces  a  large  amount  of  heat.  Burning  gas  jets  and 
oil  lamps  are  instances  in  which  both  light  and  heat  result 
from  chemical  energy.  In  fact,  all  ordinary  burning  is  due 
to  the  union  of  the  gases  of  the  air  with  a  combustible  sub- 
stance. Since  heat  causes  molecular  motion,  it  is  not  sur- 
prising to  find  that  motion  may  be  turned  to  heat ;  even  rubbing 
the  hands  together  increases  the  heat  in  them.  When  a  bullet 
strikes  a  target,  the  motion  of  the  bullet  ceases,  but  both  the 
bullet  and  the  target  are  heated.  Brakes  may  be  applied  so 


FIG.  2. — Test-tubes,  beakers,  flasks  and  stand  used  in  making  experiments. 

closely  to  car  wheels  as  to  cause  sparks  to  fly  from  them.  In 
other  days  before  matches  were  known,  fire  was  made  by 
striking  flint  a  glancing  blow  with  steel.  The  motion  of  the 
flint  against  the  steel  generated  enough  heat  to  make  small 
particles  of  the  flint  red-hot.  Even  the  air,  which  at  first 
thought  seems  too  light  and  thin  to  offer  much  resistance  to 
bodies  passing  through  it,  may  nevertheless  produce  much 
heat  in  this  way  as  in  the  case  of  the  so-called  shooting  stars, 
which,  in  their  fall  to  the  earth  become  so  hot  by  merely  rub- 


ENERGY  21 

bing  against  the  air  that  they  shine.  .  From  the  fact  that 
whenever  one  form  of  energy  disappears  another  form  appears 
in  its  place,  we  conclude  that  energy,  like  matter,  cannot  be 
destroyed. 

26.  Kinetic  and  Potential  Energy. — Upon  examination  we 
find  that  all  kinds  of  energy  fall  into  one  of  two  classes.     When 
energy  is  actually  doing  work,  as  in  water  falling  over  a  dam, 
or  the  uncoiling  of  a  spring,  we  speak  of  it  as  kinetic  energy. 
When  it  is  capable  of  work,  but  not  actually  working,  as  is  the 
water  above  the  dam,  or  the  coiled  spring,  it  is  called  potential 
energy.     Energy,  as  we  have  noted,  may  be  changed  from  one 
form  to  another,  and  it  may  also  be  transferred  from  one  body 
to  another.     In  winding  up  a  clock,  we  transfer  some  energy 
from  our  own  body  to  the  clock  spring.     If  the  clock  is  run 
by  weights,  we  transfer  energy  when  we  lift  them.     The  kinetic 
energy  expended  in  this  work  becomes  potential  energy  until 
the  clock  starts  to  run,  and  then  it  becomes  kinetic  energy 
again. 

27.  The  Source  of  Energy. — The  sun  is  the  earth's  one  great 
source  of  energy.     Engines  have  been  constructed  that  derive 
their  energy  directly  from  the  sun's  rays,  but  generally  we 
make  use  of  the  energy  in  sunlight  after  it  has  been  trans- 
formed in  various  ways.     Windmills,  for  instance,  are  turned 
by  currents  of  air  which  owe  their  direction  and  force  to  the 
unequal  distribution  of  heat  over  the  earth's  surface.     Water- 
wheels  secure  their  energy  from  falling  water  which  has  pre- 
viously been  evaporated  by  the  sun's  heat,  blown  over  ele- 
vated regions,  in  the  form  of  clouds,  and  condensed  again  as 
rain.     Peat,  coal,  oil,  and  gas  have  been  formed  from  the  re- 
mains of  plants  and  animals  of  past  ages,  which  built  up  their 
tissues  from  energy  derived  from  the  sun's  light  and  heat,  just 
as  they  are  being  built  up  at  present. 

28.  Heat  and  Light  Compared. — Heat  and  light  are  closely 
related  in  that  they  come  from  the  sun  in  the  form  of  radiant 


22  EXPERIMENTAL   GENERAL   SCIENCE 

energy,  which  travels  about  186,000  miles  a  second  and  takes 
some  eight  minutes  to  cross  the  more  than  92,000,000  miles 
that  separate  us  from  the  sun.     Radiant  energy  moves  for- 
ward in  straight  lines,  but  the  waves  of  which  it  consists 
vibrate  very  rapidly  back  and  forth  across  the  direction  of  the 
rays.     It  is  not  until  it  comes  into  contact  with  some  form  of 
matter  that  radiant  energy  becomes  heat  or  light.     The  prin- 
cipal difference  between  them  appears  to  be  that  light  rays 
are  much  more  rapid  than  heat  rays,  and  affect  a  different  one 
of  the  senses.    Light  rays  vibrate  with  inconceivable  rapidity. 
The  rays  that  give  the  sensation  of  red  vibrate  392,000,000,- 
000,000  times  a  second  and  those  which  give  the  sensation  of 
violet  vibrate  757,000,000,000,000  times  a  second.     Some  of 
the  invisible  rays  which  affect  the  photographer's  plates  and 
films  vibrate  twice  as  fast  as  the  violet  rays  (§134).     Both 
heat  and  light  rays  can  be  bent  or  reflected,  very  smooth  sur- 
faces, such  as  mirrors,  being  most  effective  in  this  respect. 
As  radiant  energy,  heat  rays  readily  pass  through  transparent 
substances,  but  when  they  strike  opaque  bodies  some  of  the 
energy  is  absorbed  as  heat.     When  the  heat  is  again  turned 
to  radiant  energy  of  a  longer  wave  length  (§77),  it  does  not 
then  pass  easily  through  even  transparent  bodies.     It  is  due 
to  this  fact  that  greenhouses  and  hot-beds  are  sometimes  called 
" traps  to  catch  sunbeams."     Most  of  the  radiant  energy 
readily  passes  in  through  the  glass  roof,  but  after  being  changed 
to  the  longer  heat  rays,  finds  escape  difficult,  and  thus  remains 
to  warm  the  plants  in  the  enclosure.     The  water  vapor  in  the 
air  acts  in  a  similar  way  to  keep  the  earth  warm,  allowing  the 
radiant  energy  to  pass  through  it,  but  preventing  the  passage 
of  the  long  heat  rays. 

Practical  Exercises 

1.  Why  does  the  snow  melt  at  the  base  of  trees  and  other  objects 
before  it  melts  in  open  fields? 


ENERGY  23 

2.  The  air  in  the  tires  of  bicycles  left  standing  in  the  sun  soon  show 
increased  pressure.     Why? 

3.  Dough  contains  bubbles  of  carbon  dioxide  gas.     How  does  the  heat 
of  the  oven  cause  the  bread  to  rise  in  baking? 

4.  Which  is  warmer,  the  water  at  the  top  of  a  water-fall  or  that  below  ? 
Why? 

6.  At  the  temperature  of  absolute  zero  there  is  no  heat  in  a  substance. 
How  would  this  affect  the  motion  of  the  molecules? 


6.  When  the  hand  is  held  in  the  sunlight  coming  through  a  window- 
pane,  it  feels  warmer  than  the  pane  does.     Why  (§28)? 

7.  Why  is  the  air  cold  at  some  distance  from  the  earth  when  the  heat 
energy  from  the  sun  passes  through  it?  - 

8.  How  does  hammering  a  piece  of  metal  affect  its  temperature? 

9.  How  does  it  affect  the  speed  of  its  molecules? 

10.  What  was  the  source  of  energy  which  caused  the  changes  noted 
in  the  foregoing  experiments? 

11.  Which  do  you  infer  would  warm  more  quickly  in  the  sunlight,  a 
board,  or  the  air  near  it? 

12.  Pick  out  the  instances  of  kinetic  and  potential  energy  in  the  fol- 
lowing list :  a  coal  fire,  driving  a  nail,  a  rock  on  a  mountain  side,  a  stick 
of  dynamite,  coasting  down  hill,  a  loaded  gun. 


CHAPTER  V 
COMPOSITION  OF  MATTER 

29.  Chemical  Elements. — In  studying  the  structure  of 
matter,  we  have  discovered  that  it  is  made  up  of  exceedingly 
small  particles  called  molecules,  but  we  have  yet  to  learn  what 
molecules  are  made  of.  Chemists  and  physicists  who  have 
investigated  this  problem  are  of  the  opinion  that  molecules 
are  composed  of  still  smaller  particles  called  atoms.  There  are, 
of  course,  as  many  different  kinds  of  molecules  as  there  are 
different  kinds  of  matter,  but  atoms  are  less  common ;  in  fact, 
there  are  only  about  eighty  different  kinds.  Since  the  mole- 
cules are  built  up  of  these  atoms,  the  differences  that  they 
exhibit  must  be  due  to  differences  in  the  number  and  kinds  of 
atoms  of  which  they  are  composed.  When  a  substance  has 
only  one  kind  of  atom  in  its  molecules,  it  is  called  a  chemical 
element.  Gold,  copper,  iron,  and  other  metals,  mercury,  sul- 
phur, carbon,  and  phosphorus  are  examples  of  chemical  ele- 
ments. According  to  our  definition,  there  can  be,  of  course, 
only  as  many  different  kinds  of  chemical  elements  as  there  are 
different  kinds  of  atoms.  Most  substances,  therefore,  are 
composed  of  more  than  one  kind  of  atom,  and  are  called 
chemical  compounds.  Often  a  very  slight  difference  in  the 
structure  of  the  molecule  may  make  a  great  difference  in  the 
substance.  For  instance,  such  substances  as  sugar,  vinegar, 
starch,  wood,  alcohol,  fat,  and  oil  are  merely  different  combina- 
tions of  the  three  chemical  elements,  carbon,  hydrogen,  and 
oxygen.  About  a  hundred  thousand  different  combinations  of 
carbon  with  other  elements  are  known. 

24 


COMPOSITION   OF   MATTER 


25 


30.  Distribution  of  the  Chemical  Elements. — The  different 
chemical  elements  are  very  unequally  distributed  in  the  earth's 
crust.  Some,  like  radium,  are  extremely  rare,  and  occur  only 
in  combination  with  other  elements.  Others  are  very  common 
and  occasionally  occur  in  the  pure  or  " native"  state.  Gold, 
silver,  copper,  and  some  of  the  other  metals  may  be  found 
native.  The  oxygen  and  nitrogen  in  the  air  are  uncombined, 
but  usually  these  elements  are  combined  with  others,  and  in  the 


FIG.  3. — Proportion  of  various  elements  in  the  earth. 

latter  state  may  be  found  in  vast  deposits.  About  95  per  cent, 
of  the  earth  is  made  up  of  the  five  elements,  oxygen,  silicon, 
aluminum,  calcium,  and  iron.  Oxygen  is  the  most  abundant  of 
the  elements  and  itself  forms  nearly  one-half  the  earth.  It 
forms  one-fifth  of  the  air,  eight-ninths  of  the  water,  and  enters 
into  a  great  many  combinations  with  other  elements.  Carbon 
is  found  in  practically  all  organic  substances;  that  is,  in  all 
substances  formed  by  living  things.  Silicon  is  the  essential 


26 


EXPERIMENTAL   GENERAL   SCIENCE 


part  of  all  sand,  sandstone,  and  quartz  rocks.  Aluminum  is 
present  in  clay,  and  calcium  is  a  necessary  component  of  all 
limestone  rocks.  Crystalline  carbon  forms  the  diamond,  and 
crystalline  aluminum  with  oxygen  forms  the  ruby,  emerald  and 
sapphire.  Corundum,  or  emery,  is  an  impure  form  of  the 
crystalline  state  of  this  compound.  The  more  common  chem- 
ical elements  are  given  in  the  accompanying  table : 


Name 

Symbol 

Name                 S 

Symbol 

Aluminum  

.   Al 

Lithium  

Li 

Antimony  (Stibium)  . 

.   Sb 

Magnesium  

Mg 

Argon  

.   Ar 

Manganese  

Mn 

Arsenic 

.   As 

Mercury        (Hydrar- 

Barium   

.    Ba 

gyrum)  

Hg 

Bismuth  

.   Bi 

Nickel  

Ni 

Boron  

.   B 

Nitrogen  

N 

Bromine  

.   Br 

Oxygen  

O 

Calcium  

.   Ca 

Phosphorus  

P 

Carbon  

.   C 

Platinum  

Pt 

Chlorine  

.   Cl 

Potassium  

K 

Cobalt  

.   Co 

Radium  

Ra 

Copper  (Cuprum) 

.   Cu 

Silicon  

Si 

Fluorine  

.   F 

Silver  (Argentum)  .  .  . 

Ag 

Gold  (Aurum)  

.   Au 

Sodium  (Natrium)  .  .  . 

Na 

Hydrogen  

.   H 

Sulphur  

S 

Iodine  

.   I 

Tin  (Stannum)  

Sn 

Iron  (Ferrum) 

.   Fe 

Tungsten  (Wolfram). 

W 

Lead  (Plumbum")  . 

Pb 

Zinc  .  . 

Zn 

31.  Chemical  Symbols  and  Formulas. — In  order  to  facilitate 
his  work  and  save  time  and  space  in  writing,  the  chemist  has  an 
abbreviation  for  each  chemical  element,  which  he  uses  instead  of 
the  name.  This  is  called  a  chemical  symbol.  The  chemical 
symbol  is  usually  the  initial  of  the  element,  but  in  cases  where 
more  than  one  element  have  the  same  initial  all  but  one  have  a 
single  letter  added.  Thus  C  always  stands  for  carbon,  while 
the  chemical  symbol  for  calcium  is  Ca,  for  copper,  Cu,  and 
for  chlorine,  Cl,  No  chemical  element  has  more  than  two  let- 


COMPOSITION    OF   MATTER  27 

ters  in  its  symbol,  and  the  second  letter  is  always  a  small  letter. 
Co  therefore,  stands  for  cobalt,  an  element,  but  CO  stands  for 
carbon  monoxide,  a  chemical  compound  of  carbon  and  oxygen. 
A  few  elements,  such  as  sodium  (Na),  silver  (Ag),  and  potas- 
sium (K),  have  symbols  which  do  not  include  their  initials. 
In  such  cases,  it  will  be  found  that  the  symbols  were  given  to 
these  substances  when  they  were  called  by  other  names.  The 
names  have  since  been  changed,  but  the  symbols  have  not.  A 
group  of  chemical  symbols  indicating  the  number  and  kind  of 
atoms  in  a  molecule  of  a  given  substance  is  called  a  chemical 
formula.  Thus  sulphuric  acid  has  the  formula  H2S04,  lime- 
stone, CaCOs,  and  orthoclase  a  common  mineral,  K  Al  Si308. 
The  chemical  symbol  when  standing  alone  is  understood  to 
indicate  a  single  atom  of  the  element;  when  there  is  more 
than  one  of  a  kind  of  atom  in  a  molecule,  the  number  is  in- 
dicated by  writing  the  number  of  atoms  below  the  line.  Thus, 
in  the  formula  for  orthoclase,  we  see  that  there  are  three  atoms 
of  silicon  and  eight  of  oxygen  in  its  molecules.  . 

32.  Chemical  Compounds. — A  chemical  compound  is  not  a 
mere  mechanical  mixture  of  two  or  more  elements,  but  is  a 
different  substance  that  often  has  properties  not  found  in  any 
of  the  elements  from  which  it  was  made.  When  sulphur  and 
iron  are  mixed  together  they  remain  a  mere  mechanical  mixture 
until  heat  is  applied.  When  heated  they  soon  form  a  new 
substance  known  as  sulphide  of  iron.  This  has  a  different 
color  from  the  substances  composing  it,  and  is  not  affected  by 
a  magnet,  though  the  iron  before  it  was  combined  was  strongly 
attracted.  It  is  not  always  possible,  however,  to  tell  in 
advance  what  sort  of  a  substance  will  be  formed  by  the  union 
of  two  or  more  elements.  The  union  of  two  gases  does  not 
necessarily  produce  a  gaseous  compound,  nor  does  the  union  of 
two  solids  always  produce  a  solid.  Water,  which  is  a  liquid 
at  ordinary  temperatures,  is  composed  of  two  gases,  oxygen 
and  hydrogen.  When  these  gases  are  free  and  uncombined, 


28  EXPERIMENTAL   GENERAL   SCIENCE 

they  cannot  be  made  liquid  except  under  great  pressure  and  at 
an  extremely  low  temperature.  Table  salt,  the  .familiar 
white  solid,  consists  of  sodium,  a  silvery  solid,  and  chlorine, 
a  greenish  and  poisonous  gas.  Still  more  remarkable  is  the 
union  of  carbon  and  sulphur  to  form  carbon  disulphide  (€82). 
Carbon  is  the  well-known  black  solid  represented  by  lamp- 
black, or  charcoal,  and  sulphur  is  a  tasteless  and  odorless  yellow 
solid.  When  combined  in  the  proportion  of  two  of  sulphur  and 
one  of  carbon,  the  result  is  a  colorless  substance  instead  of 
either  black  or  yellow,  liquid  instead  of  solid,  and  having  a 
strong  and  disagreeable  odor. 

Moreover,  charcoal  or  sulphur  alone  may  be  eaten  without 
harm,  and  are  often  taken  as  medicine,  but  when  combined  as 
carbon  disulphide  (€82),  they  are  poisonous,  and  the  suffo- 
cating gas  which  they  produce  is  often  used  to  destroy  insects 
and  other  vermin.  In  numerous  cases,  the  union  or  disinte- 
gration of  two  substances  is  influenced  by  a  third  which  does 
not  form  a  part  of  the  substance  produced.  Thus,  when  man- 
ganese dioxide  is  mixed  with  potassium  chlorate  and  heated, 
the  latter  gives  up  its  oxygen  much  more  readily  than  it  would 
by  itself.  Substances  that  influence  chemical  action  in  this 
way  are  called  catalyzers. 

33.  Proportions  of  Elements  in  Compounds. — In  forming 
the  molecules  of  a  substance,  the  chemical  elements  unite  with 
one  another  in  definite  and  unvarying  proportions.  It  is  this 
feature  that  makes  the  molecules  of  a  given  substance  all  alike, 
no  matter  how  many  chemical  elements  compose  it.  When 
carbon  and  oxygen  unite  to  form  carbon  dioxide  (€62),  two 
atoms  of  oxygen  always  unite  with  one  of  carbon.  Though 
great  quantities  of  oxygen  may  be  present,  it  does  not  affect 
the  result;  one  atom  of  carbon  will  take  on  only  two  of  oxygen. 
When  oxygen  is  scarce  however,  one  atom  of  carbon  may  unite 
with  one  atom  of  oxygen,  forming  carbon  monoxide  (CO).  We 
see,  therefore,  that  while  the  atoms  of  different  chemical  ele- 


COMPOSITION   OF  MATTER  29 

ments  do  not  unite  in  haphazard  proportions,  they  may  unite 
in  different,  though  definite,  proportions  to  form  different 
substances.  The  behavior  of  nitrogen  and  oxygen  are  instruc- 
tive in  this  connection.  Various  combinations  of  these  two 
elements  form  nitric  oxide  (NO),  nitrous  oxide  (N20),  nitro- 
gen peroxide  (N02),  nitrogen  trioxide  (N203),  and  nitrogen 
pentoxide  (N205).  The  first  two  are  colorless  gases  the  third 
is  a  red-brown  gas,  the  fourth  is  a  bluish-green  liquid,  and  the 
last,  a  white  solid,  though  all  are  made  of  different  proportions 
of  the  same  two  colorless  gases. 

34.  Chemical  Affinity. — The  force  which  causes  various  ele- 
ments to  combine,  and  holds  them  in  their  compounds,  is  called 
chemical  affinity.  This  property  is  probably  electrical  in  its 
nature.  Chemical  affinity  does  not  act  with  equal  force  in  all 
combinations,  for  in  some  the  atoms  are  so  weakly  held  to- 
gether that  they  separate  if  the  compound  is  left  standing  for 
any  length  of  time.  In  this  way,  hydrogen  peroxide  (H202) 
loses  one  of  its  atoms  of  oxygen  and  becomes  merely  water 
(H20).  This  is  the  reason  that  peroxide  of  hydrogen,  as  it  is 
called,  spoils  if  left  exposed  to  the  air  for  any  length  of  time. 
In  other  gases,  one  chemical  *may  displace  another  in  a  com- 
pound when  associated  with  it.  For  instance,  when  hydro- 
chloric acid  (HC1)  is  poured  on  limestone  (CaC03),  carbon  di- 
oxide (C02)  is  liberated,  and  the  other  atoms  form  chloride  of 
lime  and  water,  according  to  the  equation  2HC1  +  CaCO3  = 
C02  +  CaCl2  +  H20.  When  hydrochloric  acid  is  poured 
on  zinc,  the  chlorine  unites  with  the  zinc,  forming  zinc  chloride 
(ZnCl2)  and  the  hydrogen  is  released  as  a  gas.  By  a  similar 
process,  iron  is  reduced  from  its  ores.  Ordinary  iron  ores  are 
oxides  combined  with  iron.  When  such  ores  are  mixed  with 
carbon  and  heated,  the  carbon  unites  with  the  oxygen  leaving 
the  iron  free.  When  the  molecules  of  a  substance  are  acted 
upon  in  such  a  way  as  to  make  one  or  more  new  substances  by  a 
rearrangement  of  the  atoms,  we  speak  of  the  change  as  a  chem- 


30  EXPERIMENTAL   GENERAL   SCIENCE 

ical  reaction.  The  burning  of  wood  is  another  illustration  of 
chemical  reaction.  The  formula  for  cellulose  of  which  the 
wood  is  composed  is  (C6Hio05).  In  burning,  the  oxygen 
unites  with  the  carbon  to  form  carbon  dioxide  (C02),  leaving 
the  other  elements  to  form  water.  When  iron  rusts  some  of  the 
oxygen  in  the  air  unites  with  the  atoms  of  iron,  and  actually 
makes  it  heavier. 

35.  Heat  and  Chemical  Change. — Heat  is  concerned  in  all 
chemical  reactions  and  either  appears  or  disappears  when  the 
reaction  takes  place.  At  very  low  temperatures,  all  chemical 


FIG.  4. — Setting  fire  to  zinc  and  sulphur  on  piece  of  asbestos  paper. 

action  ceases.  In  some  cases,  heat  is  necessary  to  make  the 
elements  unite;  in  other  cases,  heat  applied  to  a  substance  will 
cause  it  to  break  up  into  its  elements  again;  and  in  still  other 
cases,  the  union  of  the  chemical  elements  gives  off  heat.  The 
union  of  hydrogen  and  carbon  produces  more  heat  than  the 
union  of  any  other  elements.  The  union  of  carbon  and  oxygen, 
as  in  the  burning  of  wood  and  coal  also  gives  off  much  heat. 
Sulphur  and  oxygen  uniting  give  off  much  less  heat  and  phos- 
phorus and  oxygen  still  less.  Respiration  is  a  familiar  example 
of  the  appearance  of  heat  with  chemical  change,  the  heat  being 
due  to  the  union  of  oxygen  with  the  carbon  in  our  bodies.  Cal- 
cium carbide,  used  in  making  acetylene  gas,  takes  in  much  heat 
energy  when  it  is  formed,  but  gives  it  off  again  when  the  gas 
produced  from  it  is  burned.  The  rare  element,  radium,  has 


COMPOSITION    OF   MATTER  31 

the  peculiar  property  of  giving  out  heat  and  always  remaining 
about  five  degrees  warmer  than  its  surroundings.  The  energy 
of  light  may,  like  heat,  effect  chemical  changes.  Hydrogen 
and  chlorine,  mixed  in  darkness,  give  no  reaction,  but  a  ray  of 
strong  light  will  cause  them  to  unite  with  explosive  violence. 
It  is  also  the  chemical  energy  of  light  that  affects  the  silver 
salts  of  photographic  films  and  plates  and  causes  the  pictures  to 
appear.  Light  also  causes  the  disintegration  of  hydrogen  per- 
oxide which  accounts  for  its  being  kept  in  brown  bottles  and  in 
darkness.  Energy  of  a  similar  nature  causes  our  skin  to  tan  in 
strong  sunlight. 

Practical  Exercises 

1.  Consult  the  table  of  chemical  elements  and  make  a  list  of  all  of 
those  with  which  you  are  familiar. 


2.  Make  a  list  of  all  the  uncombined  chemical  elements  that  you  can 
find  in  the  school  room. 


3.  Write  after  the  names  in  the  following  list  the  correct  chemical 
symbols : 

Iodine  Potassium  Iron 

Carbon  Oxygen  Zinc 

Mercury  Gold  Chlorine 

Tungsten  Sodium  Calcium 


4.  Write  after  the  names  of  the  following,  the  chemical  elements  of 
which  they  are  composed : 

Limestone  (CaCO3)  Washing  soda  (Na2CO8) 

Table  salt  (NaCl)  Calcium  chloride  (CaCl2) 

Sulphuric  Acid  (H2SO4) 

6.  Thoroughly  mix  one-quarter  of  a  teaspoonful  of  powdered  zinc  and 
an  equal  amount  of  powdered  sulphur.  Place  these  on  a  piece  of  asbestos 
paper  and  apply  heat  from  above  by  means  of  a  bunsen  burner  held  at 


32  EXPERIMENTAL   GENERAL   SCIENCE 

arm's  length.     The  chemical  reaction  will  produce  zinc  sulphide.     Is  this 
an  element  or  a  compound?     Why? 

6.  Of  what  use  was  heat  in  the  foregoing  experiment? 

7.  Can  you  write  the  formula  for  zinc  sulphide? 


8.  Place  a  small  quantity  of  mercuric  oxide  (HgO)  in  a  test-tube, 
and  heat  strongly.  What  change  in  the  color  of  the  substance  do  you 
notice? 


9.  What  is  left  in  the  cooler  part  of  the  test  tube  after  it  is  heated? 

10.  What  becomes  of  the  other  element? 

11.  What  did  the  application  of  heat  do  in  this  experiment? 

12.  How  did  this  experiment  differ  from  that  in  question  5? 

13.  When  a  ton  of  wood  is  burned  more  than  a  ton  of  gas  goes  up  the 
chimney.     How  do  you  explain  this? 

14.  Why  is  it  necessary  to  know  the  temperature  of  the  solutions  when 
developing  films,  prints,  and  negatives  in  photography? 

16.  Of  what  use  is  heat  in  cooking  food  other  than  softening  the 
food  and  killing  the  germs? 


CHAPTER  VI 
THE  MEASUREMENT  OF  MATTER 

36.  Standards. — Many  times  each  day  we  have  occasion  to 
measure  matter  in  various  ways.  Such  questions  as  how 
much,  how  long,  or  how  heavy,  are  continually  on  our 
tongues.  Nearly  all  buying  and  selling  involves  questions  of 
the  measurement  of  matter.  The  system  of  measurement 
with  which  we  are,  at  present,  most  familiar  makes  use  of 
such  units  as  feet,  yards,  miles,  quarts,  bushels,  tons,  pounds, 
and  the  like,  and  these  are  subdivided  entirely  without  regard 
to  uniformity,  so  that  we  have  to  remember  a  great  variety  of 
special  numbers,  containing  fractions  equally  lacking  in  uni- 
formity. There  are,  for  instance,  5^  yards  in  a  rod,  24% 
cubic  feet  in  a  perch,  while  the  numbers  that  we  use  in  square 
measurement  are  144,  9,  30J4,  160,  and  640.  On  this  account 
it  has  always  been  a  difficult  task  to  learn  the  different  tables  of 
measurement,  and  to  work  problems  in  them.  Even  scien- 
tists were  bothered  by  these  difficult  tables  and  long  ago 
invented  a  better  system.  This  latter  is  called  the  metric 
system,  and  it  is  the  one  in  common  use  in  practically  all 
civilized  countries  except  England  and  the  United  States.  In 
our  own  country,  the  use  of  this  system  has  been  legal  since 
1866,  and  though  the  old,  or  English,  system  is  still  the  com- 
mon one,  the  new  system  is  fast  gaining  in  favor,  and  is 
practically  the  only  one  now  used  in  scientific  laboratories.  So 
important  has  the  metric  system  become,  that  in  1893  two  of  its 
units,  the  meter  and  the  kilogram,  were  adopted  as  the  legal 
fundamental  standards,  and  our  yard  and  pound  are  now 
actually  standardized  by  comparison  with  them. 

33 


34  EXPERIMENTAL   GENERAL   SCIENCE 

37.  The  Advantage  of  the  Metric  System.—  The  great 
advantage  of  the  metric  system  is  that  it  is  a  decimal  system, 
in  which  ten  of  one  denomination  makes  one  of  the  next 
higher,  exactly  as  in  our  coinage.  This  renders  it  easy  to 
make  calculations  of  various  kinds,  since  one  denomination 
may  be  changed  into  terms  of  another  by  multiplying  or  divid- 
ing by  tens,  hundreds  or  thousands.  Moreover,  in  the  English 
system,  we  cannot  conveniently  express  low  denominations 
as  fractions  of  higher  ones.  In  the  metric  system,  however,  we 
have  but  to  set  the  quantities  down  in  their  order  and  insert  a 
decimal  point  at  the  proper  place.  In  this  system,  all  the 
tables  one  will  ever  need  in  measuring  lengths, 
surfaces,  weights,  and  volumes  may  be  learned 
in  a  single  morning  instead  of  requiring  months 
for  the  study  of  the  tables  as  in  the  English 
system. 

38.  The  Meter.  —  The  meter  from  which  the 
metric  system  takes  its  name  is  the  standard  of 
length.     At  the  time  it  was  established,  it  was 
Fio     5  _The  intended  to  be  one  ten-millionth  of  the  distance 
standard  meter,  from  the  equator  to  the   pole,   or  the  forty- 


millionth  part  of  a  great  circle  or  meridian.  It 
is,  therefore,  a  little  more  than  three  feet  in 
length  (39.37  inches).  For  practical  purposes,  it  is  defined  as 
the  distance,  at  the  temperature  of  melting  ice,  between  two 
lines  ruled  on  a  certain  bar  of  platinum  and  iridium  which  is 
kept  at  the  International  Bureau  of  Weights  and  Measures 
near  Paris.  Accurate  copies  of  this  bar  are  preserved  at 
Washington  and  at  the  capitals  of  many  other  countries  and 
serve  as  standards  with  which  other  measuring  instruments 
may  be  compared.  Owing  to  the  difficulty  of  exactly  repro- 
ducing these  standard  meters  by  ordinary  measurements,  if 
lost  or  destroyed,  it  is  now  proposed  to  designate  a  certain 
number  of  light  waves  as  the  length  of  a  meter.  These  light 


THE   MEASUREMENT  OF  MATTER  35 

waves  are  unvarying  and  the  exact  length  of  a  meter  can, 
therefore,  be  found  at  any  time. 

39.  Divisions  of  the  Metric  S/stem. — The  meter  is  divided 
into  tenths  (decimeters),  hundredths  (centimeters),  and  thou- 
sandths (millimeters),  the  names  of  these  divisions  being  made 
by  using  the  Latin  prefixes  deci  (10)  centi  (100),  and  milli 
(1000).  The  words  dime,  cent,  and  mill  in  our  coinage  have 
the  same  significance.  Multiples  of  the  meter  have  names 
made  by  using  the  Greek  prefixes.  Thus  ten  meters  is  a  deka- 
meter,  one  hundred  meters  a  hectometer,  and  one  thousand 
meters  a  kilometer.  Of  these  larger  divisions,  the  kilometer  is 
the  only  one  commonly  used,  smaller  lengths  being  expressed 
in  meters  or  its  divisions,  especially  centimeters  and  milli- 

CENTIMETER 

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FIG.  6. — Centimeter  and  inch  scales.     (Tower,  Smith  and  Turton.} 

meters.  In  the  measurement  of  surfaces,  since  two  dimen- 
sions are  involved,  one  hundred  (10  X  10)  of  one  division 
makes  one  of  the  next.  Thus  100  square  centimeters  makes 
a  square  decimeter,  and  100  square  decimeters  makes  a  square 
meter. 

40.  Grams  and  Liters. — The  unit  of  weight  in  the  metric 
system  is  designated  as  the  weight  of  a  cubic  centimeter  of 
pure  water  at  its  greatest  density  (4°C.).  This  unit  is  called 
the  gram.  We  can  get  some  idea  of  the  weight  of  a  gram  by 
remembering  that  our  five-cent  coin  or  nickel  weighs  five 
grams.  Like  the  meter,  the  gram  is  divided  into  tenths, 
hundredths,  and  thousandths,  and  the  names  of  the  divisions 
are  formed  by  using  the  same  prefixes.  A  thousandth  of  a 
gram,  therefore,  is  a  milligram  and  a  thousand  grams  is  a  kilo- 


36  EXPERIMENTAL   GENERAL   SCIENCE 

gram.  The  latter  is  commonly  abbreviated  to  kilo.  One 
thousand  kilograms  is  called  a  metric  ton.  The  standard  of 
volume  (or  size)  is  the  liter  (pronounced  leeter).  It  is  equal 
to  a  thousand  (10  X  10  X  10)  cubic  centimeters.  The  divi- 
sions and  multiples  of  the  liter  are  the  same  as  in  the  other 
standards.  The  denominations  most  commonly  used  are  the 
liter  and  the  hectoliter.  Instead  of  milliliters  small  quantities 
are  usually  expressed  in  cubic  centimeters  which  are  the  equiva- 
lent of  milliliters.  Instead  of  the  kiloliter  its  equivalent,  the 


FIG.  7. — Standard  kilogram.     (Black  and  Davis.} 

cubic  meter,  is  more  frequently  used.  Copies  of  the  standard 
kilogram  and  of  the  liter  are  preserved  at  the  Bureau  of  Stand- 
ards at  Washington.  This  Bureau  is  also  charged  with  a  gen- 
eral supervision  of  our  weights  and  measures.  It  not  only 
furnishes  correct  standards  of  measures  for  length,  weight,  and 
volume,  but  also  supplies  standard  thermometers,  pyrometers, 
photometers  and  many  others. 

Practical  Exercises 

1.  Construct  the  table  of  lengths  beginning  with  the  millimeter  and 
•nding  with  the  kilometer  as  follows: 


THE   MEASUREMENT  OF  MATTER  37 

10  millimeters  equal  1  centimeter 
10  centimeters  equal  1,  etc. 


2.  Construct  a  table  of  weights  beginning  with  a  milligram. 

3.  Construct  a  table  of  volumes. 

4.  Examine  a  meter  stick  and  find  out  how  many  inches  there  are 
in  a  meter. 

6.  What  unit  of  measurement  in  the  English  system  is  the  meter 
nearest  in  length? 

6.  Which  is  larger,  a  centimeter  or  an  inch? 

7.  About  how  much  larger? 

.     8.  Which  is  larger,  a  dekameter  or  a  decimeter?     How  much  larger? 


9.  Which  is  the  greater  distance,  a  kilometer  or  a  mile?     (Reduce 
to  feet  or  meters  for  comparison.) 


10.  How  many  feet  farther?     How  many  meters  farther? 

11.  How  many  square  millimeters  in  a  square  centimeter? 


12.  Using  a  pair  of  scales,  compare  a  gram  weight  with  an  ounce. 
Which  is  heavier?    How  much  heavier? 


13.  Which  is  heavier,  a  kilogram  or  a  pound?  How  much  heavier? 
(Make  this  calculation  from  what  you  know  of  the  comparat  ive  weight 
of  grams  and  ounces.) 


38 


EXPERIMENTAL    GENERAL   SCIENCE 


CC 

20lC 


14.  By  means  of  a  graduate,  measure  out  10  cubic  centi- 
meters of  water.     Is  it  more  or  less  than  a  spoonful? 


16.  How  many  cubic  centimeters  in  the  spoon  you  used  ? 

16.  Examine  a  liter  measure.     What  unit  in  the  English 
system  is  the  liter  nearest  in  size? 

17.  How  many  centimeters  in  5  meters? 

18.  How  many  milligrams  in  2  grams? 


FIG.  8.— A      19.  How  many  liters  in  a  kiloliter? 
graduate   for 
measuring 
liquids.  20    How  many  grams  in  10  kilograms'' 


CHAPTER  VII 
DENSITY  AND  SPECIFIC  GRAVITY 

41.  Weight. — It  is  a  matter  of  common  observation  that  all 
objects  of  the  same  size  are  not  equal  in  weight.     A  piece  of 
iron  is  much  heavier  than  a  piece  of  cork  of  the  same  volume. 
We  explain  this  by  saying  that  iron  is  denser  than  cork;  that 
is,  that  a  given  volume  of  iron  has  more  matter  in  it  than  an 
equal  volume  of  cork.     Since  heating  a  substance  causes  its 
molecules  to  move  farther  apart,  we  infer  that  a  given  volume 
of  a  substance  in  the  gaseous  state  will  weigh  less  than  the 
same  volume  of  it  in  the  solid  form,  and  this  is  found  to  be 
exactly  the  case.     It  weighs  less  because  there  are  fewer  mole- 
cules of  it  in  a  given  volume.     This  is  the  reason  warm  air 
rises.     Heating  it  causes  it  to  be  less  dense  and  therefore 
lighter,  and  it  is  then  pushed  up  by  the  surrounding  cooler 
and  heavier  air.     We  must  not  confuse  density  and  weight, 
however.     The  mass  of  a  body  is  the  amount  of  matter  in  it 
and  this  depends  upon  its  density,  but  the  weight  of  a  body  is 
simply  the  pull  of  the  earth  upon  it,  which,  owing  to  the  shape 
of  the  earth,  may  differ  in  different  places.     For  instance,  an 
object  weighing  589  pounds  at  the  equator  would  weigh  590 
pounds  at  the  poles.     A  body  weighing  100  pounds  on  the 
earth  would  weigh  nearly  1)^  tons  on  the  sun. 

42.  How  Density  is  Measured. — In  order  to  measure  a 
thing,  we  must  have  a  standard  with  which  to  compare  it. 
The  standard  for  measuring  the  density  of  gases  is  usually  the 
air  at  the  temperature  of  melting  ice.     For  measuring  the 
density  of  solids  and  liquids,  water  is  taken  as  a  standard. 
This  latter  makes  a  most  convenient  standard  since  it  has  been 

39 


40  EXPERIMENTAL   GENERAL   SCIENCE 

agreed  that  a  cubic  centimeter  of  water,  when  at  its  greatest 
density,  weighs  a  gram.  If  we  know  the  density  of  a  substance, 
that  is,  if  we  know  how  much  a  cubic  centimeter  of  it  weighs 
in  comparison  with  water,  we  can  easily  ascertain  its  weight 
by  finding  its  volume  in  cubic  centimeters  and  multiplying 
this  by  its  density.  Suppose  for  instance  that  a  body  has  a 
density  of  5.  This  means  that  a  cubic  centimeter  of  it  weighs 
five  times  as  much  as  a  cubic  centimeter  of  water,  or  five 
grams.  If  we  had  a  volume  of  ten  cubic  centimeters,  it  would 
weigh  5  times  10,  or  50  grams.  The  density  of  a  solid  may 
be  determined  in  the  first  place  by  weighing  it  in  air  and  again 
in  water.  The  second  weighing  is  accomplished  by  attaching 
it  to  a  balance  in  such  a  way  that  it  is  immersed  in  the  water 
during  the  weighing.  A  substance  weighed  in  water  weighs 
less  than  it  does  in  air,  and  this  difference  in  weight  is  the 
weight  of  the  water  it  displaces  when  immersed.  In  this  way, 
we  find  the  weight  of  a  volume  of  water  equal  to  the  volume 
of  the  solid,  and  when  this  is  compared  with  its  weight  in  air, 
we  have  its  density.  Suppose  the  weight  in  air  of  a  given 
substance  to  be  9  grams,  and  a  loss  of  3  grams  in  weight  is 
discovered  when  it  is  weighed  in  water.  It  is  very  evident 
that  the  water  it  displaced  must  weigh  3  grams,  and  that  the 
substance  is  therefore  three  times  as  heavy  as  the  same  vol- 
ume of  water;  that  is,  it  has  a  density  of  3.  Though  it  is 
usually  more  convenient  to  express  density  in  grams  per  cubic 
centimeter,  we  are  not  confined  to  that  manner  of  expression 
since  density  is  a  relative  term.  It  can  be  as  easily  expressed 
in  grams  per  cubic  foot,  cubic  inch,  or  other  volumes.  Gold 
has  a  density  of  19.3,  therefore  a  cubic  foot  of  gold  would 
weigh  19.3  times  as  much  as  a  cubic  foot  of  water,  and  a  cubic 
yard  of  gold  would  of  course  be  19.3  times  as  heavy  as  a  cubic 
yard  of  water. 

43.  Specific  Gravity. — The  term  specific  gravity  is  often 
used  to  indicate  the  weight  of  substances  in  comparison  with 


DENSITY   AND    SPECIFIC    GRAVITY 


41 


equal  bulks  of  water.  The  heavier  the  substance,  the  greater 
its  specific  gravity  is  said  to  be.  This  term,  however,  is 
rapidly  passing  out  of  use  since  the  unit  of  mass  in  the  metric 
system  is  defined  as  the  weight  of  a  cubic  centimeter  of  water 
at  its  greatest  density.  In  this  system,  therefore,  the  true 
density  of  a  body  and  its  density  with  reference  to  water  is 
the  same  thing.  The  density  of  liquids  is  often  measured  by 
a  specific  gravity  bottle  made  of  thin  glass.  This  is  first  weighed 
when  empty,  then  when  filled  with  water,  and  again  when 


FIG.  9. — Common  hydrometer.     (Duff.)     FIG.  10. — Specific  gravity  bottle  ' 

filled  with  the  liquid  to  be  tested.  In  this  way,  the  weights 
of  the  two  liquids  are  easily  compared.  A  common  way  of 
measuring  the  density  of  a  liquid  is  by  means  of  a  hydrometer 
which  is  essentially  a  sealed  glass  tube  so  weighted  that  it  will 
sink  to  a  certain  depth  in  pure  water.  In  liquids  more  dense 
than  water,  it  will  of  course  not  sink  so  deep,  and  in  lighter 
liquids  it  will  sink  deeper.  By  means  of  a  scale  on  the  tube, 
the  differences  and  therefore  the  densities,  are  indicated. 
Hydrometers  for  measuring  single  liquids  have  special  names 
which  are  often  self-explanatory;  as  alcoholometer,  saccharome- 


42 


EXPERIMENTAL   GENERAL   SCIENCE 


ter,  lactometer,  and  salimeter.  Since  the  purity  of  a  substance 
has  a  close  relation  to  its  density,  these  special  forms  of  hy- 
drometers are  much  used  commercially  in  fixing  the  value  of 
liquids. 

44.  Buoyancy. — When  a  body  sinks  in  a  medium  lighter 
than  itself,  the  medium  in  which  it  sinks  pushes 
upward  on  the  body  with  a  force  exactly  equal 
to  the  weight  of  the  medium  displaced.     This 
force  pushing  upward  is  called  buoyancy,  and  a 
body  which  is  supported  in  this  way  is  said  to 
be  buoyant.     Cork,  owing  to  its  small  density, 
is  very  buoyant  in  water,  and  is  much  used  in 
life-preservers.     It  is  due  to  the  buoyancy  of 
the  air,  that  balloons,  filled  with  some  lighter 
gas,  rise  irt  it,  and  balloons  are  therefore  said  to 
FIG.  11.— The  De  buoyant.     It  is  owing  to  buoyancy  also  that 
diving  vial  (small  one  can  lift  a  stone  in  water  which  he  would 
bottle  of  water)6  ^n(^  impossible  to  move  on  land.     An  instruct- 
ive illustration  of  the  principle  involved  may 
be  made  of  a  good-sized  bottle  and  a  small  vial.     Fill  the  large 
bottle  with  water  and  invert  in  it  the  small  vial,  taking  care  to 
have  just  enough  air  in  the  latter  to  keep  it  afloat.     When  the 
large  bottle  is  full  of  water  and  the  cork  pushed  in,  it  will  com- 


FIG.   12. — Spirit  level. 

press  the  air  in  the  vial,  make  more  room  for  the  water,  and 
cause  it  to  sink.  Removing  the  pressure  will  allow  the  air  in  the 
small  vial  to  expand  and  push  out  some  of  the  water  making 
it  lighter  and  causing  it  to  rise  to  the  surface.  Submarines 


DENSITY   AND    SPECIFIC    GRAVITY 


43 


are  maneuvered  under  water  by  varying  the  weight  of  the  boat 
in  a  somewhat  similar  way.  The  spirit  level  used  by  carpenters 
and  masons  consists  essentially  of  a  glass  tube  full  of  liquid,  ex- 
cept for  a  small  bubble  of  air.  This  air  being  lighter  than  the 
liquid,  always  comes  to  the  top.  When  the  tube  in  its  setting 
is  placed  on  a  level  surface  the  bubble  will  of  course  come  to 
rest  exactly  in  the  middle  of  the  tube.  Any  variation  from 
this  position  indicates  a  surface  that  is  not  level. 


TABLE  OF  DENSITIES 


Alcohol  
Aluminum 
Copper  
Cork  
Glass  

.      .79 
.   2.58 
.   8.80 
.      .24 
.   2.60 

Cast  iron  
Chloroform  
Ether 

.   7.40 
.   1.52 

72 

Carbon  dioxide  . 
Hydrogen  

.      .00 
.      .001 

2  58 

Lead 

11  30 

8  80 

Nickel 

.    .     8.90 

.24 

Oak  

80 

2.60 

Olive  oil      .  .  . 

91 

7  40 

Silver 

10  53 

1.52 

Tin  

7.29 

72 

Zinc 

7  15 

.001978 

Nitrogen 

.001256 

.0000896 

Oxveen  .  . 

.00143 

Practical  Exercises 

1.  Fill  a  graduate  half  full  of  water,  and  drop  into  it  any  convenient 
piece  of  metal,  finding  the  volume  by  noting  carefully  the  amount  of 
water  it  displaces.     Then  weigh  the  metal.     Assuming  that  every  cubic 
centimeter  of  water  displaced  weighs  a  gram,  does  the  weight  of  the 
metal  justify  the  specific  gravity  assigned  to  it  in  the  table? 

2.  Which  is  heavier  gold  or  silver?     How  much  heavier? 

3.  The   density   of   brass  is  8.5.     How  many  centimeters  of  water 
would  be  necessary  to  exactly  balance  4  cubic  centimeters  of  brass? 


4.  How  many  grams  would  10  cc.  of  platinum  weigh  if  the  density 
of  platinum  is  21.5? 


44  EXPERIMENTAL  GENERAL   SCIENCE 

6.  A  cubic  foot  of  water  weighs  62.3  pounds.     Could  you  carry  a 
cubic  foot  of  gold?    How  much  would  it  weigh? 


6.  Aluminum  is  often  called  a  light  metal.     Will  it  float  or  sink  in 
water? 


7.  A  vessel  10  by  10  by  10  cc.  in  size  would  hold  how  many  grams 
of  water? 


8.  How  many  grams  of  mercury  would  the  above-mentioned  vessel 
hold? 


9.  Find  the  weight  of  a  liter  of  alcohol. 

10.  How  much  heavier  is  a  cubic  centimeter  of  iron  than  one  of  cork? 

11.  Which  has  the  greater  specific  gravity,  cream  or  milk?    How  do 
you  know? 

12.  Which  weighs  more,  a  cubic  centimeter  of  ice  or  a  cubic  centimeter 
of  water.     How  do  you  know? 

13.  Do  you  infer  that  ice  has  or  has  not  a  density  greater  than  1? 

14.  Why  does  olive  oil  float  on  water? 

15.  Will  iron  float  or  sink  in  mercury?     Why? 


16.  Housewives  often  test  the  strength  of  brine  by  putting  an  egg  in 
it.     An  egg  will  sink  in  pure  water.     Explain  why  it  will  float  hi  brine. 


17.  When  the  smoke  from  chimneys  does  not  rise  readily,  is  the  air 
light  or  heavy?    How  do  you  know? 


DENSITY   AND   SPECIFIC    GRAVITY  45 

18.  In  which  would  a  boat  sink  deeper,  a  river  or  the  ocean? 

19.  If  the  ice  man  leaves  a  piece  of  ice  50  by  40  by  10  cm.  in  size  has 
he  left  50  pounds  or  not?     (Ice  has  a  specific  gravity  of  .9.) 

20.  A  liter  of  hydrogen  weighs  about  .09  gram.     How  much  heavier 
is  water  than  hydrogen? 

21.  If  a  body  sinks  half  of  its  volume  in  water,  what  is  its  specific 
gravity? 

22.  What  is  its  specific  gravity  if  it  sinks  half  its  volume  in  mercury? 

23.  In  which  should  it  be  easier  to  swim,  salt  or  fresh  water?     Why? 

24.  With  what  force  does  gravity  attract  a  kilogram  weight? 


CHAPTER  VIII 
THE  MEASUREMENT  OF  TEMPERATURE 

45.  How  Measured. — In  the  measurement  of  temperature, 
we  have  to  deal  with  the  effects  of  an  addition  of  energy  to 
matter.     It   is   more   convenient   to   measure   the   effect   of 
energy  upon  matter  than  to  measure  the  energy  direct.     The 
instrument  with  which  we  now  ascertain  the  temperature  of  an 
object  is  called  a  thermometer.     This  instrument  was  not  in- 
vented until  about  a  hundred  years  after  Columbus  discovered 
America.     Before  that  time,  people  had  to  depend  upon  their 
bodily  feelings  for  information  of  this  nature  and  such  methods 
are  still  in  use  for  roughly  estimating  temperature,  as  when  we 
touch  an  object  with  the  hand  to  see  if  it  is  warm  or  cold. 
This,  however,  is  a  very  unreliable  method  of  testing  because 
our  temperature  sense  is  easily  deceived.     If  we  hold  one  hand 
in  a  basin  of   hot  water  for  a  time  and  the  other  hand  in  a 
basin  of  cold  water,  and  then  put  both  hands  into  a  vessel 
of  water  at  room  temperature,  the  hand  that  was  in  the  hot 
water  will  now  feel  cold  and  the  one  that  was  in  the  cold 
water  will  feel  warm,  though  they  are  both  in  water  of  the 
same  temperature  (§83). 

46.  The  Therommeter. — Thermometers  may  be  made  of 
any  substance  that  expands  and  contracts  quickly  with  varia- 
tions in  temperature,  but  the  substances  most  used  are  mer- 
cury and  alcohol.     The  ordinary  thermometer  consists  of  a 
slender  glass  tube  closed  at  the  upper  end,  with  a  bulb  at  the 
lower  end  containing  either  of  the  two  liquids  mentioned.     If 
alcohol  is  used,  it  is  generally  colored  so  that  it  may  be  more 

46 


THE   MEASUREMENT  OF   TEMPERATURE 


47 


easily  seen.  A  scale,  by  means  of  which  the  changes  may  be 
read,  is  either  marked  on  the  glass  tube  or  firmly  attached  to  it. 
The  scale  is  marked  off  in  many  small  divisions  called  degrees, 
which  serve  as  units  of  measurement. 

47.  Graduating  the  Thermometer. — Before  the  thermom- 
eter can  be  used,  the  scale  must  be  adjusted  to  the  height  of 
the  liquid  in  the  tube.  In  making  this  adjustment,  two  con- 
venient fixed  points  from  which  to  measure 
are  found  in  the  temperature  at  which  water 
boils  and  the  temperature  at  which  it  freezes. 
After  the  liquid  has  been  put  into  the  tube, 
the  bulb  is  placed  in  melting  ice  which  causes 
the  column  of  liquid  to  contract  and  shorten. 
The  point  where  the  top  of  the  column  comes 
to  rest  is  marked  freezing.  Then  the  bulb  is 
placed  in  the  steam  from  water  boiling  under 
certain  standard  conditions  until  the  liquid 
column  again  comes  to  rest.  This  point  is 
marked  boiling.  The  distance  between  the 
two  points  is  then  marked  off  in  degrees. 
Cheap  thermometers  are  made  with  less  care 
and  their  temperature  points  determined  by 
comparison  with  the  scale  of  a  more  exact 
instrument.  The  ordinary  thermometer  is  ?]G-  13.— Centi 

,,     ,  .  grade  and    Fahren- 

called  a  Fahrenheit  thermometer  after  the  heit  thermometers, 
man  who  invented  it.  On  this  thermometer,  (Tower,  Smith  and 
the  scale  begins  at  a  point  called  zero  (0) 
which  is  32  degrees  below  the  freezing  point.  The  boiling  point 
is  marked  212,  thus  making  180  degrees  between  the  freezing 
and  boiling  points.  A  much  better  scale  is  that  called  the 
Centigrade  scale  in  which  the  freezing  point  is  marked  zero 
and  the  boiling  point  100.  This  is  a  decimal  scale  similar  to 
others  already  studied  and  is  used  almost  universally  for  scien- 
tific work.  Its  employment  for  other  uses  is  steadily  increas- 


48 


EXPERIMENTAL   GENERAL   SCIENCE 


ing  and  in  time  it  is  probable  that  it  will  completely  displace 
the  Fahrenheit  scale.  It  is  to  be  noted  that  the  differences  in 
these  two  scales  are  not  differences  in  temperature  but  merely 

differences  in  methods  of  measuring. 
Thirty-two  degrees  above  zero  Fah- 
renheit (32°F.)  is  the  same  as  zero 
Centigrade  (0°C.).  Thermometers 
are  frequently  made  with  both  scales 
marked  on  them. 

48.  Absolute  Zero. — The  maker  of 
the  Fahrenheit  thermometer  appears 
to  have  assumed  that  nothing  could 
be  colder  than  32  degrees  below  the 
ther-  freezing  point  of  water,  and  for  this 
reason  he  called  that  point  zero. 
Temperatures  much  below  zero  are 
now  known.  Even  the  temperature  of  the  air  in  winter  in 
the  Northern  States  may  go  several  degrees  below  this  point. 


FIG.     14.— Clock 
mometer.      (Tower, 
and  Turton.) 


Smith 


FIG.  16. — A  recording  thermograph. 

It  is  obvious,  however,  that  an  object  cannot  go  on  losing 
heat  forever.  Sooner  or  later  the  last  trace  of  heat  disap- 
pears and  all  molecular  motion  ceases.  This  point  is  called 


THE   MEASUREMENT   OF  TEMPERATURE  49 

absolute  zero.  Temperatures  of  absolute  zero  have  never  been 
reached  on  the  earth,  but  from  the  fact  that  all  gases  contract 
one  two-hundred-and-seventy-third  of  their  volume  at  0°C. 
for  each  Centigrade  degree  of  further  cooling,  it  is  inferred 
that  absolute  zero  must  be  273  degrees  below  the  zero  of  the 
Centigrade  scale,  or  as  we  commonly  express  it— 273°C.  A 
third  temperature  scale  called  the  absolute  scale  begins  at  the 
absolute  zero  and  has  degrees  of  the  same  size  as  those  in  the 
Centigrade  scale.  On  this  scale,  therefore,  the  freezing  point 
of  water  is  273°  above  zero. 

49.  Changing  from  Fahrenheit  to  Centigrade. — With  two 
thermometer  scales  in  common  use,  it  frequently  becomes 


FIG.  16. — Thermostat. 

necessary  to  change  temperatures  from  one  scale  to  the  other. 
This  is  easily  done  when  the  relative  size  of  the  degrees  is 
considered.  From  the  fact  that  there  are  180  degrees  between 
freezing  and  boiling  on  the  Fahrenheit  scale  and  only  100  on 
the  Centigrade,  we  perceive  that  the  ratio  of  the  sizes  of  the 
two  degrees  must  be  as  180  is  to  100;  that  is,  the  Fahrenheit 
degree  is  rive-ninths  of  a  Centigrade  degree.  Therefore,  to 
change  Fahrenheit  degrees  to  Centigrade  degrees,  we  multi- 
ply by  %,  and  to  change  Centigrade  to  Fahrenheit  we  multi- 
ply by  %.  This,  however,  is  done  only  when  comparing  the 
degrees.  In  matters  of  temperature,  we  must  make  allowance 
for  the  difference  in  the  zeros  of  the  two  scales.  Thus,  when 


50  EXPERIMENTAL   GENERAL   SCIENCE 

we  turn  Fahrenheit  degrees  to  Centigrade,  we  must  subtract  32 
degrees  before  multiplying  by  %  and,  in  the  reverse  process,  we 
add  32  after  we  have  multiplied  by  %.  A  convenient  ex- 
pression of  this  method  is  as  follows:  (C.  X  %)  +  32  =  F. 
and  (F.—  32)  X  %  =  C.  For  temperatures  below  zero  Centi- 
grade, 32  degrees  must  be  subtracted  after  the  change  to  Fah- 
renheit is  made,  but  when  changing  in  the  other  direction  32 
must  first  be  added  for  all  temperatures  below  zero  Fahrenheit. 
50.  Other  Thermometers. — Long  before  the  temperature 
of  absolute  zero  is  reached,  alcohol  and  mercury  become  solid 
and  are  therefore  not  adapted  to  measuring  extremely  low 


FIG.   17. — Maximum  and  minimum  thermometers.      (Duff.) 

temperatures.  In  the  other  direction,  there  are  temperatures 
much  higher  than  boiling  water,  boiling  alcohol,  or  even  boiling 
mercury.  For  measuring  such  temperatures,  other  thermom- 
eters are  needed.  One  instrument  makes  use  of  nitrogen  or 
hydrogen  gas.  Since  the  pressure  of  a  gas  is  proportional  to  its 
temperature,  any  difference  in  pressure  may  be  translated  into 
differences  of  temperature.  The  clock  thermometer  indicates 
the  temperature  by  means  of  a  pointer  moving  over  a  dial. 
The  motion  is  given  to  the  pointer  by  strips  of  two  different 
metals  fastened  together.  These  metals  have  different  rates 
of  contracting  and  expanding  and  thus  bend  each  other  back 


THE  MEASUREMENT  OF  TEMPERATURE       51 

and  forth  with  changes  in  temperature  and  so  move  the  pointer. 
The  thermostat  so  often  used  in  regulating  the  temperature  of 
buildings  makes  use  of  a  thermometer  of  this  kind.  As  the 
temperature  changes,  the  moving  tip  opens  or 
closes  an  electric  circuit  which  operates  the 
dampers  of  the  heating  system.  When  the  pointer 
carries  a  pen  and  makes  a  continuous  record  on  a 
moving  strip  of  paper,  it  is  called  a  thermograph. 
The  indicator  of  the  thermograph  may  also  be 
moved  by  the  expansion  of  alcohol  in  a  flattened 
and  curved  metal  tube.  When  the  alcohol  ex- 
pands, the  tube  is  straightened  out  and  this  moves 
the  pointer.  The  maximum  thermometer  is  de- 
signed to  indicate  the  highest  temperature  to  which 
it  has  been  exposed  during  a  given  period.  In 
such  an  instrument,  a  constriction  just  above  the 
bulb  allows  the  mercury  to  squeeze  through  but 
will  not  allow  it  to  flow  back  again.  The  clinic 
thermometer  used  by  all  physicians  is  a  maximum 
thermometer.  Such  instruments  are  set  by  shak- 
ing the  mercury  down  into  the  bulb  again.  The 
minimum  thermometer  is  an  alcohol  thermometer 
having  a  small  indicator  in  the  tube  which  is 
drawn  down  as  the  alcohol  recedes  but  is  not 
pushed  upward  when  the  alcohol  rises.  The 
minimum  thermometer  must  be  placed  in  a  nearly 
horizontal  position.  Its  index  may  be  set  with  a 

magnet  or  by  giving  the  instrument  a  slight  jar.  clinical  ther- 
mometer. 
Practical  Exercises  (Duff.) 

1.  Examine  the  nearest  thermometer.     Is  it  made  with  mercury  or 
alcohol? 


2.  How  many  Centigrade  degrees  equal  45  Fahrenheit  degrees? 


52  EXPERIMENTAL   GENERAL   SCIENCE 

3.  How  many  Fahrenheit  degrees  equal  40  Centigrade  degrees? 


4.  Find  the  temperature  of  the  school  room  in  ^Fahrenheit  degrees 
and  change  to  Centigrade  temperature. 


5.  Express  the  temperature  of  the  blood  in  Centigrade  degrees. 


6.  Water  at  the  temperature  of  4°C.  is  at  its  greatest  density.     What 
temperature  on  the  Fahrenheit  scale  is  this? 


7.  The  protoplasm  of  living  parts  of  plants  is  killed  at  about  122°F. 
At  what  temperature  Centigrade  are  plants  killed? 


8.  Mercury   boils    at  357°C.     How   hot  is  this  on  the  Fahrenheit 
scale? 


9.  What  temperature  is  0°F.  on  the  Centigrade  scale? 


10.  What  is  the  highest  point  reached  by  the  Fahrenheit  thermometer 
in  summer  in  your  region?  What  is  the  lowest  point  reached  in  winter? 
How  many  Centigrade  degrees  would  this  difference  equal? 


11.  White-hot  iron  has  a  temperature  of  about  2200°F.     What  is  its 
temperature  Centigrade? 


12.  The  temperature  of  the  electric  furnace  is  about  4000°C.     How 
hot  is  this  on  the  Fahrenheit  scale? 


13.  Most  seeds  will  not  sprout  until  the  temperature  reaches  41°F. 
How  warm  is  this  on  the  Centigrade  scale? 


14.  What  temperature  is  absolute  zero  on  the  Fahrenheit  scale? 


THE   MEASUREMENT   OF  TEMPERATURE  53 

16.  What  would  be  the  temperature  of  boiling  water  in  Centigrade 
degrees  if  the  Centigrade  scale  began  at  absolute  zero? 


16.  What  would  be  the  temperature  of  boiling  mercury  on  the  absolute 
scale? 


17.  What  temperature  is  -40°C.  on  the  Fahrenheit  scale? 

18.  If  the  thermometer  bulb  were  made  of  a  substance  that  expands 
faster  than  mercury,  what  effect  would  this  have  on  the  column  of 
mercury? 


19.  When  the  thermometer  bulb  is  plunged  into  hot  water  the  mercury 
at  first  falls.     Why? 


20.  The  temperature  of  the  sun  is  estimated  to  be  about  7000°C 
How  hot  is  this  on  the  Fahrenheit  scale? 


CHAPTER  IX 
EFFECT  OF  HEAT  ON  VOLUME 

61.  Cohesion. — The  force  which  attracts  the  molecules  of  a 
substance  to  one  another  is  called  cohesion.  It  is  this  force 
which  we  must  overcome  in  splitting  or  pulling  a  thing  apart, 
and  which  gives  hardness,  definite  shape,  and  solidity  to  differ- 
ent substances.  Heat  weakens  cohesion  by  increasing  the 
speed  of  the  molecules  and  causing  them  to  move  farther 
apart.  Liquids  when  heated  expand  or  increase  in  volume 
more  readily  than  solids,  and  gases  more  readily  than  either. 
When  heat  is  withdrawn  from  a  body,  cohesion  draws  the 
molecules  together  again  and  causes  it  to  contract. 

52.  Melting  Point. — If  sufficient  heat  is  added  to  a  solid,  a 
point  is  finally  reached  when  cohesion  is  overbalanced.  The 
substance  then  ceases  to  have  a  definite  shape  and,  breaking 
down,  becomes  a  liquid,  or  as  we  say,  it  melts.  It  is  not  pos- 
sible to  say  in  advance  at  what  temperature  an  unknown 
substance  will  melt,  but  when  this  point  is  once  determined,  we 
may  be  sure  that  the  substance  will  always  melt  at  this  tem- 
perature under  similar  conditions.  Different  substances,  as 
might  be  assumed,  have  different  melting  points,  but  these 
points  for  each  substance  do  not  vary  unless  the  conditions 
are  changed.  Crystalline  substances,  that  is,  those  which  form 
crystals  on  solidifying,  show  most  sharply  the  changes  from  the 
solid  to  the  liquid  state.  A  few  substances  such  as  glass,  pitch 
and  wax,  do  not  have  definite  melting  points  but  slowly  soften 
under  the  influence  of  heat  and  form  a  pasty  mass.  On  the 
other  hand,  certain  other  substances,  such  as  iodine  and  cam- 
phor, do  not  melt  at  all  under  ordinary  conditions  but  appear 

54 


EFFECT  OF  HEAT  ON  VOLUME  55 

to  jump  at  once  from  a  solid  to  a  gas.  Such  a  change  of  state  is 
called  sublimation  (§89).  At  low  temperatures,  even  ice  may 
sublimate.  When  gases  of  this  kind  are  sufficiently  cooled, 
they  return  directly  to  the  solid  state.  Under  proper  condi- 
tions however,  these  substances  may  also  be  made  to  assume 
the  liquid  state. 

53.  Expansion  of  Gases. — If  sufficient  heat  is  added  to  a 
liquid  it  becomes  a  gas.     When  water  assumes  this  condition, 
we  say  it  has  evaporated.     While  liquids  are  known  to  occupy 
more  space  than  the  solids  from  which  they  were  made,  the 
most  conspicuous  examples  of  increase  of  volume  with  change 
of  state  are  found  among  the  gases.     Water  turned  to  gas 
(steam)  increases  more  than  1600  times  its  volume.     Engineers 
roughly  express  it  by  saying  that  "A  cubic  inch  of  water  makes 
a  cubic  foot  of  steam."     Another  familiar  example  of  a  solid 
that  takes  up  much  space  when  turned  to  gas  is  gunpowder. 

54.  Effects  of  Withdrawing  Heat. — Withdrawing  heat  from 
a  substance  has  exactly  the  opposite  effect  upon  its  volume 
that  heating  it  has.     All  gases  may  be  made  liquid  by  with- 
drawing heat,  but  the  process  is  hastened  by  pressure.     With  a 
reduction  in  temperature  there  always  goes  a  reduction  in 
volume,  and  this  reduction  continues  through  the  liquid  and 
solid  states  of  practically  all  substances.     Water,  however,  is 
a  conspicuous  and  important  exception.     Solid  water  (ice),  like 
other  solids,  contracts  with  a  lowering  of  the  temperature,  and 
liquid  water  contracts  like  other  liquids,  but  just  before  the 
point  at  which  it  turns  from  a  liquid  to  a  solid  is  reached 
(about  4°C.),  it  begins  to  expand,  and  as  it  turns  to  a  solid, 
it  exerts  a  pressure  of  more  than  100  tons  to  the  square  foot. 
This  pressure  is  sufficient  to  burst  water  pipes,  split  open 
rocks,  and  disturb  the  foundations  of  buildings.     It  is  to  be 
observed  that  the  pressure  is  exerted  only  at  the  instant  of 
becoming  solid.     After  this  condition  is  reached,  ice  contracts 
with  loss  of  heat,  as  other  substances  do. 


56  EXPERIMENTAL   GENERAL   SCIENCE 

56.  Casting. — A  large  number  of  metal  objects  are  ham- 
mered into  shape  but  the  majority  are  "cast"  by  being  melted 
and  poured  into  moulds.  Sharp  castings  cannot  be  made  of 
most  metals  for  the  reason  that  they  contract  on  solidifying. 
Brass  and  cast  iron  are  two  common  substances  that  expand 
slightly  in  turning  from  the  liquid  to  the  solid  state  and  so 
are  prime  favorites  with  the  foundry  man.  Type  metal  is  a 
mixture  of  various  metals  that  expands  on  solidifying,  though 
the  metals  alone  contract  on  cooling.  The  expansion  of  type 
metal  is  highly  desirable;  in  fact,  the  several  metals  composing 
it  are  selected  with  this  end  in  view,  for  if  it  did  not  expand  on 
solidifying,  it  would  not  fill  the  moulds  and  form  the  sharp 
outlines  so  necessary  for  type.  Gold  and  silver,  on  the  con- 
trary, contract  on  solidifying,  and  coins  cannot  be  cast  of 


FIG.  19. — Ring  and  ball  set. 

these  metals.  When  coins  are  made,  therefore,  pieces  of  the 
metal  have  to  be  forced  into  dies  under  great  pressure  to  give 
them  the  proper  sharpness.  Of  all  the  common  metals,  zinc 
contracts  most  when  heat  is  withdrawn. 

56.  Some  Practical  Applications. — The  expansion  and  con- 
traction of  all  substances  with  changes  of  temperature  make 
it  necessary  to  take  this  into  account  daily  in  many  operations. 
Sometimes  we  take  advantage  of  it,  as  when  steel  girders  are 
fastened  together  with  red-hot  rivets  which  contract  and  tighten 
as  they  cool;  sometimes  considerable  ingenuity  must  be  devel- 
oped to  avoid  its  effects.  Large  steel  bridges  expand  so  much 
in  the  summer  sunshine  that  the  sections  are  mounted  on  rollers 
or  have  telescoping  joints  to  permit  them  to  change  in  length. 
Long  bridges  sometimes  vary  more  than  a  foot  in  length  in 


EFFECT  OF  HEAT  ON  VOLUME 


57 


a  day.     In  stringing  telegraph,  telephone,  and  other  wires, 

the  temperature  must  also  be  considered.     If  drawn  too  tight 

on  a  hot  day  the  wires  may  shorten  and  snap  on  a  cold  one. 

Long  runs  of  steam  pipes  have  to  have  " expansion  joints"  at 

intervals  to  take  up  the  extra  length  of  the  pipe  when  heated. 

In  late  fall  and  early  spring,  plants  are  often  killed  by  being 

"heaved  by  the  frost."     That  is,  during  a  thaw, 

water  accumulates  about  them  and  in  freezing 

expands  and  lifts  them  out  of  the  ground.     In 

the  same  way,  foundations  may  be  damaged  if 

they  are  not  carried  down  into  the  earth  below 

the  frost  line.     Expansion  caused  by  the  frost 

breaks  up  rocks  into   soil   and   makes  plant 

growth  possible.    Land  is  often  plowed  late  in 

fall  to  permit  of  this  mellowing  action  of  the 

frost.     Since  solids  and  liquids  differ  from  gases 

and  do  not  expand  alike,  it  is  often  necessary 

to  make  a  nice  choice  of  materials  in  order  to 

insure  the  proper  working  of  our  machines. 

Invar,  a  compound  of  steel  and  nickel,  often 

called    nickel-steel,   expands    very  little  with 

changes  of  temperature  and  is   therefore   an 

ideal  substance  from  which  to  make  measuring 

instruments,  clock  pendulums,  scales,  and  the 

like.     If   pendulums   were   made  of  ordinary  ^FlG'    20;~ 

*  .  *    Compensated 

metals  they  would  be  too  long  in  summer  and  mercury  pendu- 
cause  the  clock  to  run  slow.     In  winter  with  the  l"m:  [Black  and 

Dctvis.) 

same  pendulum  the  clock  would  run  too  fast. 
In  good  clocks,  the  pendulum  is  often  made  of  two  different 
metals  with  different  rates  of  expansion  so  that  one  counter- 
acts the  effects  of  the  other.  Alcohol  and  mercury,  on  the 
other  hand,  rapidly  change  in  volume  with  changes  in  tem- 
perature and  thus  are  useful  in  thermometers.  In  electric 
light  bulbs  the  current  must  be  carried  to  the  filament  by 


58  EXPERIMENTAL   GENERAL   SCIENCE 

wires  which  have  practically  the  same  rate  of  expansion  as 
the  glass  bulbs  themselves.  Platinum,  though  very  expen- 
sive, is  the  most  suitable  metal  for  this  purpose  since  it  ex- 
pands and  contracts  at  nearly  the  same  rate  as  glass.  Other 
metals  would  contract  and  let  air  into  the  bulb  or  expand  and 
break  it.  In  pouring  hot  liquids  into  glass,  as  in  canning,  the 
inside  of  the  jar  often  expands  so  rapidly  that  the  jar  is  cracked 
before  the  outside  can  become  heated  and  expand  to  match  it. 
For  a  similar  reason  a  drop  of  cold  water  splashed  on  a  hot 
glass  may  break  it  by  causing  the  part  to  cool  and  contract 
too  suddenly.  Crucibles  made  of  quartz  expand  and  contract 
very  little  with  changes  of  temperature  and  when  heated  red 
hot  may  be  plunged  into  water  without  being  broken. 

Practical  Exercises 

1.  Heat  the  ball  of  a  ring-and-ball  set  for  a  short  time  and  try  to  pass 
it  through  the  ring.     Explain  the  effect  noted. 

2.  Fill  a  florence  flask  with  water  and  cork  with  a  one-hole  stopper 
through  which  passes  a  close-fitting  glass  tube.     Put  the  flask  on  a  piece 
of  wire  gauze  over  a  bunsen  burner  and  heat.     Explain  the  movement 
of  the  water  in  the  tube.  . 

3.  Empty  out  the  water  from  the  flask  used  in  the  preceding  experi- 
ment and  stop  up  the  glass  tube  with  a  drop  of  any  liquid.     Warm  the 
flask  by  holding  the  hand  upon  it.     Explain  the  results  noted. 

4.  Hold  the  mouth  of  a  tall  cylinder  or  large  bottle  at  some  distance 
above  a  flame  until  the  air  within  has  been  thoroughly  warmed.     Then 
quickly  place  the  vessel,  mouth  down,  in  a  dish  of  water.     Explain 
how  the  cooling  of  the  air  in  the  vessel  makes  more  room  for  water  in  it. 

6.  Could  one  make  a  thermometer  of  water? 

6.  When  the  sun  shines  on  a  tall  chimney  or  monument,  will  it  bend 
toward  or  away  from  the  sun?     Why? 


EFFECT   OF   HEAT   ON  VOLUME 


59 


7.  Why  is  it  necessary  in  indicating  the  exact  length  of  the  standard 
meter  to  mention  the  temperature  of  the  standard  (§38)? 

8.  Give   a   reason   for  the  space  left  between  the  ends  of  rails  on 
railroads. 

9.  Stoppers  sometimes  become   so  firmly  fixed  in  bottles  that  it  is 
impossible  to  loosen  them  with  the  hands.     Can  you  suggest  a  method 
of  loosening  them  based  on  what  you  have 

learned  in  this  lesson? 

10.  Given  a  liter  of  water  at  a  temperature 
of  50°.     Will  it  take  up  more  or  less  space  if 
heated  to  a  temperature  of  90°? 

11.  Would  heating  have  any  effect  on  the 
total  weight  of  water? 

12.  Would  a  cupful  of  water  at  50°  weigh 
as  much  as  or  more  than  a  cupful  of  water 
heated  to  90°? 

13.  How  do  you  think  a  cubic  foot  of  air 
at  zero  would    compare  in  weight  with  a 
cubic  foot  of  air  when  the  mercury  stands 
at  100°? 


14.  Would  you  expect  to  get  a  pound  of 
water  from  a  pound  of  ice? 


FIG.  21 — Wire  gauze 
placed  under  glass  flask 
when  heating  it. 


15.  Why  may  test-tubes,  beakers  and  the  like,  made  of  thin  glass, 
be  heated  without  breaking,  when  fruit  jars  and  tumblers  cannot? 

16.  Would  fruit  jars  be  as  likely  to  crack  when  hot  liquids  are  put 
into  them  if  the  jars  were  slowly  warmed  to  the  temperature  of  the  liquids 
first?     Why? 


17.  From  what  you  know  of  heat  and  its  effects  do  you  think  cold  is 
a  form  of  energy  or  merely  the  absence  of  heat? 


CHAPTER  X 
HEAT  AND  CHANGE  OF  STATE 

57.  The  Calorie. — The  temperature  of  a  body  is  not  neces- 
sarily an  indication  of  the  amount  of  heat  it  contains.     A  small 
pool  on  a  summer  day  may  be  warmer  than  the  nearest  lake, 
and  yet  anybody  can  understand  that  the  lake  must  have  a 
much  larger  amount  of  heat  in  it.     The  thermometer  merely 
indicates  the  temperature  of  a  body.     To  measure  the  total 
amount  of  heat  in  it,  we  need  a  new  standard  of  comparison. 
Such  a  standard  is  found  in  the  calorie,  which  is  defined  as  the 
amount  of  heat  necessary  to  raise  the  temperature  of  one  gram 
of  water  one  degree  Centigrade.     Since  all  substances  give  off 
as  much  heat  in  cooling  as  they  took  up  in  warming,  our  calorie 
could  as  well  have  been  defined  as  the  amount  of  heat  that 
must  be  withdrawn  to  lower  the  temperature  of  one  gram  of 
water  one  degree  Centigrade.     Another  unit  of  heat  some- 
times called  the  large  calorie  is  a  thousand  times  larger  than 
the  calorie  we  have  discussed.     This  latter,  however,  is  more 
properly  called  the  kilocalorie. 

58.  Specific  Heat. — When  we  add  equal  amounts  of  heat  to 
equal  weights  of  different  substances,  we  discover  that  all  do 
not  increase  in  temperature  at  the  same  rate;  that  is,  it  takes 
more  heat  to  raise  a  gram  of  some  substances  one  degree  in 
temperature  than  it  does  others.     The  amount  of  heat  that 
will  raise  a  kilogram  of  water  one  degree  Centigrade  will  raise 
an  equal  weight  of  copper  ten  degrees,  of  silver  or  tin  twenty 
degrees,  and  of  mercury  thirty  degrees.    Land  heats  up  four 
times  as  fast  as  water.     The  amount  of  heat  required  to  raise 
the  temperature  of  any  substance  one  degree  in  comparison 

60 


HEAT   AND    CHANGE    OF   STATE  61 

with  the  heat  required  to  raise  the  same  amount  of  water  one 
degree  is  called  its  specific  heat.  Specific  heat  is  like  specific 
gravity  in  that  water  is  taken  as  a  standard  for  comparison. 

TABLE  OF  BOILING  POINTS  IN  CENTIGRADE  DEGREES 


Air  

-180 

Hydrogen  

-253 

Alcohol  
Ammonia  

78 
-34 

Mercury  
Oxygen  

357 
.    -183 

Ether  
Lead  

35 
1525 

Sulphur  
Zinc  

444.6 
918 

TABLE  OP  SPECIFIC  HEATS 

Alcohol 60       Iron , 12 

Aluminum .  : 22       Mercury 033 

Copper 094    Water 1.00 

Ice 50      Zinc 093 

TABLE  OF  MELTING  POINTS  IN  CENTIGRADE  DEGREES 

Alcohol -130     Iron 1530 

Aluminum 658     Mercury —39 

Brass 910    Silver 961 

Copper 1083     Tin 232 

Gold 1063     Zinc 419 

With  the  exception  of  hydrogen,  water  has  the  highest  specific 
heat  of  any  known  substance.  It  is  this  quality  that  makes 
water  so  valuable  in  steam  and  hot  water  heating,  hot- water 
bags,  and  the  like.  The  large  amount  of  heat  needed  to  raise 
it  to  the  boiling  point  must  all  be  given  out  before  it  can  re- 
sume its  original  temperature.  The  high  specific  heat  of 
water  also  has  an  important  effect  on  the  daily  temperature. 
The  moisture  in  the  air,  by  warming  and  cooling  slowly,  pre- 
vents sudden  or  rapid  changes  in  temperature.  This  also  ex- 
plains the  mild  climate  of  regions  near  large  bodies  of  water. 
In  summer  they  are  cooler  than  places  further  inland  because 
much  of  the  heat  goes  to  warm  the  water,  and  in  winter  they 
are  warmer  because  the  heat  taken  up  by  the  water  is  now 


62  EXPERIMENTAL   GENERAL   SCIENCE 

given  back  to  the  air.  The  British  Islands,  though  in  the  lati- 
tude of  Labrador,  have  a  much  milder  climate  because  of  the 
Gulf  Stream  which  flows  past  their  shores.  One  reason  why 
water  puts  out  fires  is  because  the  heat  needed  to  warm  it 
reduces  the  temperature  below  the  point  at  which  the  fire  will 
burn. 

59.  Latent  Heat. — Although  a  calorie  of  heat  is  said  to  raise 
a  gram  of  water  one  degree  Centigrade,  when  the  boiling  point 
is  reached  this  statement  needs  qualifying.  We  then  discover 
that  the  addition  of  another  calorie  does  not  turn  the  boiling 
water  to  steam,  nor  does  it  raise  its  temperature  one  degree; 
in  fact,  it  is  not  until  536  more  calories  are  added  that  the  water 
will  turn  to  steam,  and  then  the  steam  is  the  same  temperature 
as  the  boiling  water.  In  other  words,  it  requires  536  times  as 
much  heat  to  turn  a  gram  of  water  to  steam  as  it  does  to  raise 
its  temperature  one  degree.  Five  hundred  and  thirty-six  cal- 
ories seems  thus  to  have  disappeared  or  become  latent  during 
the  change  of  state.  When  we  recall  the  effect  ,of  heat  on  the 
motion  of  molecules,  however,  we  realize  that  the  heat  energy 
has  not  really  disappeared  but  is  employed  in  holding  the  mole- 
cules farther  apart.  That  this  is  true  is  shown  by  the  fact 
that  when  the  gas  (steam)  contracts  and  turns  back  to  a  liquid 
again,  the  536  calories  reappear  as  heat.  A  similar  state  of 
affairs  exists  at  the  point  where  water  freezes.  When  a  gram 
of  water  turns  to  ice,  it  gives  off  80  calories,  though  the  ice  is 
then  no  colder  than  the  water  from  which  it  was  made.  When 
the  ice  is  melted,  however,  80  calories  of  heat  are  required  to 
be  put  into  it  to  effect  the  change  of  state,  and  the  water  still 
has  the  temperature  of  zero;  that  is,  80  calories  of  heat  have 
become  latent  in  the  process.  In  a  certain  sense,  therefore, 
melting  may  be  said  to  be  a  cooling  process  and  freezing  a 
warming  process  since  in  melting  each  gram  of  water  absorbs 
80  calories  and  in  freezing  it  gives  off  this  heat.  All  substances 
act  like  water  with  reference  to  heat  when  a  change  in  state 


HEAT  AND    CHANGE    OF   STATE  63 

occurs,  though  in  none  of  them  are  such  large  quantities  of 
heat  involved.  The  heat  which  is  absorbed  or  given  out 
with  a  change  of  state-  is  usually  spoken  of  as  latent  heat. 
The  scientists  call  it  the  heat  of  fusion  when  solids  turn  to 
liquids,  and  the  heat  of  vaporization  when  liquids  turn  to  gases. 
Though  water  at  zero  Centigrade  ordinarily  turns  to  ice  when 
80  calories  of  heat  per  gram  are  withdrawn  from  it,  it  is  possible 
to  cool  it  still  more  and  have  it  remain  liquid  df  it  is  not  agi- 
tated. As  soon  as  it  is  stirred,  however,  part  of  it  turns  to  ice 
and  the  remainder  returns  to  the  temperature  of  zero.  This 
is  the  way  in  which  "anchor  ice"  is  formed  at  the  bottom  of 
rivers.  The  water  becomes  super-cooled  in  the  stretches  of 
quiet  water  above  a  rapid  and  when  the  rapid  is  reached  the 
movement  of  the  water  causes  the  formation  of  anchor  ice 
which  may  frequently  be  seen  clinging  to  the  stones  beneath 
the  water. 

TABLE  OF  LATENT  HEATS 

In  boiling  In  melting 

Air 47  Copper 30 

Alcohol 206  Ice 80 

Ether 91  Iron 35 

Mercury 62  Platinum 27 

Sulphur 262  Tin 14 

Water 536 

60.  Practical  Applications. — In  steam-heating  systems,  the 
water  is  turned  to  steam  in  a  boiler  located  in  the  basement  or 
other  convenient  place  and  is  then  carried  in  pipes  to  the  rooms 
to  be  heated.  In  the  radiators,  it  gives  up  its  latent  heat  and 
becomes  liquid  again,  then  runs  back  to  the  boiler  and  is  re- 
heated. Something  of  the  kind  is  provided  by  nature  on  a 
much  larger  scale  in  autumn  evenings  when  the  moisture  in 
the  air  turns  to  fog  and,  in  giving  up  its  latent  heat,  protects 
tender  vegetation  from  the  cold.  Farmers  sometimes  utilize 
the  latent  heat  in  water  by  placing  tubs  of  the  liquid  in  cellars 


64  EXPERIMENTAL   GENERAL   SCIENCE 

to  prevent  freezing.     Not  until  the  water  in  freezing  has  given 
up  its  latent  heat  is  there  danger  to  other  things  in  the  cellar. 

Practical  Exercises 

1.  When    a    substance    is  boiling,   does  the  addition  of  more  heat 
increase  its  temperature  or  merely  cause  it  to  boil  faster? 

2.  How  does  this  knowledge  enable  one  to  save  gas  in  cooking? 

3.  How  warm  can  ice  be  made?     Why? 

4.  How  would  you  attempt  to  make  mercury  solid? 
6.  How  could  iron  be  made  liquid? 

6.  What  do  you  infer  as  to  the  temperature  of  liquid  air? 

7.  What  inference  do  you  make  as  to  the  temperature  of  liquid  iron? 


8.  Would  you  expect  the  boiling  point  of  liquid  air  to  be  above  or 
below  zero  Fahrenheit? 


9.  In  a  substance  which  can  exist  in  all  three  states,  which  has  the 
most  heat  in  it,  the  solid,  the  liquid,  or  the  gaseous  form? 

10.  Which  contains  the  least  heat? 


11.  Dissolve  about  100  grams  of  sodium  thiosulphate  (the  "hypo" 
of  the  photographer)  in  about  10  cubic  centimeters  of  boiling  water, 
heating  until  all  is  dissolved.  Place  in  a  florence  flask,  cover  and  set 
away  until  cool.  .Then  drop  into  the  liquid  a  crystal  of  the  hypo. 
What  effect  has  this  on  the  state  of  the  substance? 


12.  Account  for  the  heat  that  appears  in  the  foregoing  experiment. 


HEAT  AND    CHANGE   OF   STATE  65 

13.  When  snow  falls  the  weather  usually  moderates.     Why  (§58)? 

14.  In  a  "double  boiler,"  the  receptacle  containing  the  substance  to 
be  heated  is  placed  hi  a  larger  vessel  containing  water.     How  does  the 
water  in  the  second  vessel  prevent  the  burning  of  the  substance?     (How 
warm  can  water  be  made  in  an  open  vessel?) 

15.  Liquid  air  in  an  open  vessel  cannot  be  made  warmer  than  —  182°C. 
Why? 

16.  Why  do  not  all  the  ice  and  snow  melt  as  soon  as  the  temperature 
rises  above  the  freezing  point? 

17.  Which  contains  the  more  heat,  1000  gallons  of  boiling  water  or  the 
nearest  lake  at  zero?     Explain. 

18.  How  many  calories  will  be  required  to  raise  the  temperature  of 
10  grams  of  water  five  degrees  Centigrade? 

19.  Which  would  require  more  heat,  to  melt  five  grams  of  ice  or  to 
raise  five  grams  of  water  50°  hi  temperature? 

20.  If  the  temperature  of  100  grams  of  boiling  water  is  reduced 
twenty  degrees  how  many  calories  are  given  off? 

21.  If  180  calories  are  taken  from  a  gram  of  boiling  water  what  will 
be  its  temperature? 

22.  Which  has  the  greater  amount  of  heat  in  it,  1000  cubic  centimeters 
of  water  at  10°C.   or  1000   cubic   centimeters   of  iron   at  the  same 
temperature? 

23.  Why  is  copper  not  as  good  as  iron  for  making  flat-irons  used  in 
ironing  (§58)? 

24.  Why  is  an  aluminum  kettle  better  than  an  iron  one  for  heating 
water? 

5 


CHAPTER  XI 


PRESSURE  AND  CHANGE  OF  STATE 

61.  Boiling  Affected  by  Pressure. — In  previous  studies,  we 
have  discovered  that  heating  a  substance  causes  it  to  expand 
by  pushing  its  molecules  further  apart.  We  know  also  that  if 
the  heating  is  continued  long  enough,  most  substances  become 
gases  and  take  up  a  much  greater  space  ( §53) .  When  anything 
happens  to  prevent  this  expansion,  how- 
ever, it  naturally  affects  the  change  of 
state  and  requires  much  more  heat  to 
accomplish  it.  Under  ordinary  condi- 
tions, water  boils  at  sea  level  at  a  tem- 
perature of  100°C.,  but  when  the  pres- 
sure of  the  air  over  water  is  doubled,  we 
must  raise  the  temperature  to  121°C. 
before  boiling  occurs.  Reducing  the 
pressure  has  of  course  the  opposite  effect. 
If  the  air  over  an  evaporating  liquid  is 
pumped  away,  it  will  boil  at  a  very  low 

FIG.  22.— Boiling  under  f  , '     f  . ,  , , 

diminished  pressure  effect-  temperature;  in  fact,  if  the  pressure  is 

ed  by  cooling  air  in  bottom  properly  regulated  water  may  be  boiled 

and  frozen  at  the  same  temperature. 

In  boiling  syrup  and  other  thick  liquids,  which  there  is  danger 
of  burning,  they  are  often  placed  in  closed  vessels  and  the 
vapor  pumped  away.  This  not  only  lowers  the  boiling  point 
but  enables  them  to  boil  faster  (§89,  104).  An  understanding 
of  these  facts  enables  us  to  ascertain  the  height  of  different 
places  above  sea  level  by  simply  boiling  pure  water  there. 
As  we  ascend  above  sea  level,  we  rise  above  part  of  the  air 

66 


PRESSURE    AND    CHANGE    OF   STATE  67 

and  thus  the  pressure  is  reduced  and  the  boiling  point  is  corre- 
spondingly lowered.  Under  ordinary  conditions  the  boiling 
point  is  lowered  1°C.  for  each  960  feet  above  sea  level.  The 
change  of  solids  to  the  liquid  state  is  also  affected  by  pressure. 
The  interior  of  the  earth  is  believed  to  be  hot  enough  to  melt 
all  known  rocks,  and  yet  it  cannot  become  liquid  because  of 
the  enormous  pressure  upon  it. 

62.  Compression  of  Gases. — Solids  and  liquids  differ  as 
regards  the  rate  at  which  they  expand  when  heated,  but  all 
gases  expand  alike.     For  a  rise  of  1°C.  in  temperature,  they 
increase  one  two  hundred  and  seventy-third  of  their  volume  at 
0°C.     Gases,  being  perfectly  elastic,  tend  to  expand  indefinitely 
if  unconfined,  and  when  subjected  to  pressure  expand  as  soon 
as  the  pressure  is  removed.     When  enclosed,  the  molecules  are 
always  evenly  distributed  through  the  available  space,  no 
matter  what  its  size  or  shape.     When  another  gas  is  introduced 
into  the  same  space,  it  also  becomes  evenly  distributed  through 
it.     Compressing  the  gas,  however,  develops  pressure  and  the 
higher  the  temperature  of  the  gas  the  greater  the  pressure  will 
be,  since  the  myriads  of  rapidly  moving  molecules  constantly 
beat  upon  the  retaining  walls.     Liquids  are  practically  incom- 
pressible, but  gases  readily  yield  to  pressure.     If  the  tempera- 
ture remains  the  same,  doubling  the  pressure  on  a  gas  will 
cause  it  to  become  half  its  original  size,  and  trebling  the  pres- 
sure will  make  it  one-third  its  size,  and  so  on.     The  physicist 
explains  this  by  the  statement  that  "the  volume  of  a  gas  varies 
inversely  as  the  pressure  to  which  it  is  subjected."     At  a  given 
temperature  and  pressure  a  cubic  centimeter  of  any  gas  will 
have  the  same  number  of  molecules  in  it. 

63.  Heat  and  Compression. — Not  only  will  pressure  hinder 
a  liquid  from  turning  to  a  gas,  but  if  sufficient  pressure  be 
applied  it  may  even  be  caused  to  turn  back  to  the  liquid 
again.     When  pressure  is  applied  to  a  gas,  however,  a  certain 
amount  of  heat  develops  and  most  gases  cannot  therefore  be 


68  EXPERIMENTAL  GENERAL  SCIENCE 

liquefied  by  pressure  alone.  A  good  illustration  of  the  heat 
that  develops  when  a  gas  is  compressed  may  be  found  when  air 
is  pumped  into  a  bicycle  or  automobile  tire.  After  a  few 
strokes  of  the  pump  the  tube  connecting  the  pump  and  tire 
becomes  noticeably  warmer.  When  gas  under  pressure  is 
allowed  to  expand,  however,  the  molecules  at  once  move 
further  apart  and,  taking  up  some  of  the  heat  in  the  process, 
become  cooler.  As  might  be  inferred,  liquids  exposed  to  gases 
under  pressure  absorb  much  more  than  they  otherwise  would. 
The  carbonated  water  used  at  soda  fountains  consists  of  carbon 
dioxide  forced  into  the  water  under  pressure. 

64.  The  Pressure  Cooker. — In  the  pres- 
sure cooker,  which  consists  of  a  vessel  with 
a  close-fitting  cover  that  allows  no  steam 
to  escapa  advantage  is  taken  of  the  fact 
that  pressure  retards  a  change  of  state  and 
causes  an  increase  in  the  temperature  of  a 
substance.  The  contents  of  such  a  cooker 
may  be  heated  to  temperatures  of  250°F.  or 
more  and  thus  be  quickly  cooked.  A  valve 
FIG.  23.— Pressure  in  the  cover  prevents  the  pressure  from  be- 
coming  high  enough  to  cause  an  explosion. 
A  similar  contrivance  used  in  the  scientific 
laboratory  is  called  an  autoclave.  Housewives  make  use  of 
this  principle  when  they  cover  the  kettle  in  which  food  is 
cooking.  In  canning,  the  use  of  the  pressure  cooker  enables 
one  to  preserve  many  substances  that  are  otherwise  very  diffi- 
cult to  keep.  The  great  heat  to  which  they  are  thus  subjected 
kills  the  germs  of  decay  that  are  often  unharmed  by  ordinary 
processes  of  canning. 

65.  Refrigeration. — All  our  mechanical  systems  of  refrig- 
eration are  based  on  the  relations  of  pressure  and  heat  to  the 
change  of  state.  The  cooling  desired  is  accomplished  by  com- 
pressing a  gas  until  it  becomes  liquid  and  then  removing  the 


PKESSUKE   AND    CHANGE    OF  STATE 


69 


heat  from  it  by  means  of  a  stream  of  running  water  flowing 
over  the  pipes  in  which  it  is  compressed.  When  the  cooled 
liquid  is  allowed  to  expand  and  become  a  gas  again,  it  takes 
the  heat  necessary  for  this  process  from  the  substances  to  be 
cooled.  The  gas  commonly  used  is  ammonia  or  sulphur 
dioxide.  After  the  gas  has  been  compressed  and  cooled,  it 
is  allowed  to  expand  into  other  pipes  surrounded  by  strong 
brine.  The  brine  thus  cooled  is  pumped  away  to  the  place 
where  refrigeration  is  desired.  The  gas  is  used  over  and  over 
again,  the  refrigerating  system  being  so  arranged  that  the 


FIG.  24.- 


-The  air  pump  for  removing  air  from  the  bell-jar  .R. 
and  Turton.) 


(Tower,  Smith 


pump  which  compresses  it  in  one  set  of  pipes  also  serves  to 
remove  it  from  the  set  of  pipes  into  which  it  expands.  This 
process  also  reduces  the  pressure  in  the  pipes  where  expansion 
occurs. 

66.  Other  Uses  of  Pressure. — The  fact  that  a  compressed 
gas  expands  instantly  when  pressure  is  removed  is  often  taken 
advantage  of  in  engineering  operations.  By  admitting  air 
under  pressure  to  first  one  side  and  then  the  other  of  a  piston 
moving  in  a  cylinder,  motion  is  developed  which  will  run  drills 
and  riveting  machines  and  do  much  other  useful  work.  The 


70  EXPERIMENTAL   GENERAL   SCIENCE 

brakes  on  street  cars  and  railway  trains  are  set  by  compressed 
air  stored  in  a  tank  under  each  car  and  controlled  by  the  motor- 
man  or  engineer.  Pneumatic  tubes  for  carrying  mail  and  other 
light  articles  are  also  operated  by  compressed  air.  The  steam 
engine  derives  its  power  from  water  vapor  under  pressure. 
This,  usually  called  steam,  is  fed  into  a  cylinder  at  just  the 
right  times  to  give  the  piston  a  back  and  forth  motion  which  is 
turned  into  a  rotary  motion  at  the  driving  wheels.  The  gas 
engine  so  familiar  from  its  use  in  automobiles,  pumps  and  the 
like,  operates  in  the  same  way  through  energy  derived  from 
gasoline.  Since  the  pressure  in  this  type  of  engine  is  derived 
from  explosions  of  gasoline  in  the  cylinders  themselves,  it  is 
called  an  internal-combustion  engine.  Steam  under  pressure  is 
also  used  to  run  certain  engines  called  turbines,  which  are  essen- 
tially large  wheels  containing  an  immense  number  of  curved 
blades  enclosed  in  a  case.  The  steam  is  admitted  at  many 
points  in  such  a  way  as  to  strike  these  blades  and  cause  the 
wheel  to  revolve  rapidly.  A  similar  contrivance  makes  use  of 
the  energy  in  falling  water. 

Practical  Exercises 

1.  Fill  a  florence  flask  half  full  of  water  and  heat  over  the  bunsen 
burner  until  it  boils.  Remove  from  the  fire,  cork,  and  invert  on  some  con- 
venient support  such  as  a  ring  stand.  Then  pour  some  cold  water  on  the 
bottom  of  the  flask.  This  causes  the  air  within  to  cool.  How  does  this 
affect  its  pressure? 


2.  How  does  it  affect  the  boiling  point?     Why? 


3.  Why   can   you   not  raise  the  temperature  of  boiling  water  in  an 
open  vessel  to  100°C.  in  your  locality  (§104)? 


4.  Why  does  it  take  longer  to  cook  potatoes  in  Denver  than  it  does 
in  New  Orleans? 


PRESSURE    AND    CHANGE    OF   STATE  71 

5.  Would  the  pressure  cooker  be  of  any  advantage  in  Denver?    Why? 

6.  When  air  is  allowed  to  bubble  up  through  a  tall  cylinder  of  water, 
the  bubbles  get  larger  as  they  rise.     Why? 

7.  Explain  why  a  bottle  of  "charged  water"  or  "soft  drinks"  over- 
flows as  soon  as  the  cork  is  pulled. 

8.  At  what  time  of  the  year  is  the  cork  in  the  ammonia  bottle  likeliest 
to  pop  out? 

9.  Would  it  be  possible  to  use  air  in  place  of  ammonia  in  refrigeration? 

10.  Water  boils  on  Mount  Blanc  at  183°F.     At  Denver,  Colorado,  it 
boils  at  203°F.     Which  place  is  the  higher? 

11.  Air  is  often  compressed  over  water  in  tanks  for  the  purpose  of 
lifting  the  water  to  a  higher  level.     Sometimes  the  system  fails  to  work 
because  most  of  the  air  has  disappeared.     Explain  (§63). 

12.  Fill  a  large  bottle  half  full  of  water,  cork  with  a  one-hole  stopper 
through  which  a  glass  tube  extends  down  into  the  water.     With  one 
breath  blow  in  as  much  air  as  possible.     Explain  what  happens  (§62). 

13.  How  is  the  elasticity  of  the  air  made  use  of  in  automobile  and 
bicycle  tires,  air  cushions,  and  the  like? 

14.  How  is  compressed  air  made  use  of  in  the  air  gun  or  pop  gun? 


CHAPTER  XII 
COMBUSTION  AND  OXIDATION 

67.  Activity  of  Oxygen. — Oxygen  is  the  most  active  of  the 
chemical  elements,  and  forms  compounds  with  nearly  all  of 
them.     So  great  is  its  affinity  for  some,  that  it  tears  them  from 
other  compounds  in  which  they  happen  to  be,  and  thus  causes 
many  substances  to  break  down  or  disintegrate.     Most  metals, 
if  left  exposed  to  the  air  especially  in  damp  surroundings,  soon 
begin  to  unite  with  oxygen.     Thus  iron  rusts,  and  lead  and 
various  other  metals  tarnish.     Gold,  silver,  and  platinum  do 
not  readily  unite  with  oxygen  and  thus  are  in  great  demand  for 
ornaments  and  the  like.     Other  metals  are  often  covered  with 
gold  or  silver  to  prevent  tarnishing  (§173).     A  freshly  quarried 
stone  or  a  newly  sawed  board  soon  loses  its  fresh  look  and  be- 
comes dull  by  the  action  of  oxygen  upon  it.     Our  bodies  are 
kept  warm  by  the  slow  union  of  oxygen  with  the  carbon  in 
our  tissues,  and  all  ordinary  burning  is  simply  a  more  rapid 
union  of  these  two  elements.     It  must  not  be  assumed,  how- 
ever, that  the  union  of  oxygen  and  carbon  is  the  only  union 
of  this  kind  that  produces  great  heat.     One  of  the  hottest 
flames  known  is  produced  by  the  union  of  oxygen  and  hydrogen 
and,  strangely  enough,  the  result  of  this  union  is  water. 

68.  Heat  and  Light  from  Oxidation. — Whenever  oxygen 
unites  with  another  substance,  the  process  may  be  called  oxi- 
dation, though  this  term  is  commonly  reserved  for  cases  in 
which  the  union  is  not  accompanied  by  the  emission  of  per- 
ceptible light  or  heat,  as  when  iron  rusts.     When  sensible  heat 
and  light  appear,  as  in  the  burning  of  wood,  coal,  gas,  and  oil, 
we  usually  call  it  combustion.     The  only  difference,  however, 

72 


COMBUSTION  AND   OXIDATION  73 

is  that  one  proceeds  more  rapidly  than  the  other.  When 
metals  rust,  or  wood  decays,  the  total  amount  of  heat  devel- 
oped is  the  same  as  if  the  substance  had  been  burned  more 
rapidly.  If  plenty  of  oxygen  is  available,  it  may  unite  with 
other  substances  so  rapidly  as  to  raise  their  temperature  to  a 
point  where  they  glow,  or  it  may  even  cause  them  to  change 
to  gases  and  burst  into  flame.  All  flames  are  burning  gases 
of  some  kind.  A  flame,  however,  does  not  necessarily  pro- 
duce much  light.  Light  results  only  when  substances  are 
heated  'very  hot  or  to  the  condition  which  is  described  as  white 
heat.  The  calcium  light  often  used  in  stereopticons  is  pro- 
duced by  heating  a  pencil  of  lime  white-hot  in  the  flame  from 
burning  hydrogen.  The  bright  light  from  the  Welsbach  gas 
light  is  due  to  the  mantle  being  heated  to  incandescence  by 
the  burning  gas  within  it.  In  ordinary  gas  jets  and  in  the 
flame  from  wood,  coal,  oil,  and  the  like,  the  light  is  due  to 
very  hot  particles  of  unburned  carbon.  When  the  burning  is 
so  managed  that  all  the  carbon  is  oxidized,  as  in  the  bunsen 
burner,  very  little  light  results.  In  pure  oxygen  glowing  char- 
coal bursts  into  flame  and  even  iron  and  other  metals  burn 
readily.  If  it  were  not  for  the  fact  that  the  oxygen  of  the  air 
is  diluted  with  four  times  its  volume  of  nitrogen,  building  a 
fire  in  the  stove  would  probably  result  in  a  disastrous  conflagra- 
tion (§105). 

69.  Kindling  Temperature. — In  oxidation,  as  in  other  chem- 
ical reactions,  a  certain  amount  of  heat  is  found  necessary  to 
induce  the  change.  Most  substances  will  not  burn  at  ordinary 
temperatures,  but  must  first  be  heated  to  their  kindling  tem- 
perature. This  temperature  is  different  for  different  sub- 
stances. That  of  anthracite,  for  instance,  is  much  higher 
than  that  of  wood.  Some  substances,  such  as  phosphorus, 
readily  oxidize  and  burst  into  flame  when  exposed  to  the  air  at 
ordinary  temperature.  In  the  laboratory,  phosphorus  has  to 
be  kept  under  water,  oil,  or  similar  substances  to  protect  it 


74  EXPERIMENTAL   GENERAL   SCIENCE 

from  the  air.  When  a  substance  bursts  into  flame  of  its  own 
accord,  the  process  is  called  spontaneous  combustion.  It  occa- 
sionally happens  that  the  heat  generated  by  piles  of  dead 
leaves,  oily  rags,  damp  straw,  manure  piles,  and  the  like,  in- 
stead of  passing  off  into  the  air,  accumulates  in  the  material 
until  the  kindling  temperature  is  reached,  when  the  material 
begins  to  burn  by  spontaneous  combustion.  Numerous  mys- 
terious fires  have  been  traced  to  this  cause.  Spontaneous 
combustion  often  occurs  in  hay-mows,  especially  if  the  hay 
was  not  thoroughly  dried  before  storing.  Even  piles  of  fine 
coal  may  take  fire  in  this  way.  Thorough  ventilation  does 
much  to  avert  the  danger  from  such  fires. 

70.  Explosions. — When  oxygen  unites  very  rapidly  with 
another  substance,  especially  in  a  closed  space,  an  explosion 
is  the  result.     Unexpected  explosions  occurring  in  valuable 
material  may  be  most  destructive,  but  when  controlled,  ex- 
plosions are  sources  of  much  useful  power.     In  general,  the 
more  thoroughly  the  air  is  mixed  with  the  substance,  the 
greater  the  explosion  is  likely  to  be.     Gases,  therefore,  are 
more  explosive  than  liquids.     If  a  burning  match  be  thrust 
into  kerosene  oil  it  will  be  put  out,  but  the  gas  from  kerosene 
explodes  at  once  if  the  flame  reaches  it.     Air  filled  with  fine 
dust  from  flour,  coal,  starch,  wood,  or  other  substances  may 
cause  explosions.     In  the  gas  engine,  the  power  is  produced 
by  a  series  of  explosions  in  the  cylinders.     Gunpowder  and 
other  high  explosives  consist  of  a  mixture  of  substances  which 
oxidize  almost  instantly,  the  oxygen  for  this  purpose  being 
supplied  by  some  of  the  ingredients  in  the  mixture.     By  means 
of  the  gases  produced,  projectiles  may  be  fired  from  guns, 
buildings  and  other  structures  blown  up,  and  rocks  torn  to 
pieces  (§66). 

71.  Products    of    Combustion. — Nearly    all    combustible 
materials  contain  both  carbon  and  hydrogen,  and  these,  unit- 
ing with  oxygen,  produce  on  the  one  hand  carbon  dioxide  (C02), 


COMBUSTION   AND    OXIDATION 


75 


and  on  the  other  water  (H20) .  Hydrogen  gas  burning  by  itself 
produces  no  carbon  dioxide  of  course.  In  many  cases  even 
when  hydrogen  is  present,  carbon  only  is  oxidized  and  the 
hydrogen  unites  with  the  oxygen  in  the  material  to  form  water. 
Smoke  is  not  a  product  of  burning.  On  the  contrary,  it  con- 
sists of  particles  of  unburned  carbon  which,  if  allowed  to 
escape  into  the  air,  is  a  waste  of  good  material.  All  fires  should 
be  so  stoked  as  to  prevent  smoke  from  escaping.  When  soft 
coal  is  burned  at  home,  wetting  the  coal  aids  in  reducing  the 
smoke.  Though  ashes  are  left  when  coal  and  wood  are  burned, 
these  are  not  products  of  burning.  They  simply  represent  the 


FIG.  25. — A  common  way  of  preparing  oxygen. 

mineral    matter    which    was    mixed    with    the    combustible 
material. 

72.  Preparing  Oxygen  and  Carbon  Dioxide. — There  are 
various  simple  methods  of  preparing  oxygen  for  study.  A 
little  water  added  to  a  few  cubic  centimeters  of  sodium  peroxide 
(Na202)  in  a  bottle  or  jar  will  result  in  the  immediate  liberation 
of  oxygen.  The  gas  may  also  be  obtained  by  pouring  a  small 
quantity  of  hydrogen  peroxide  over  a  few  crystals  of  potassium 
permanganate.  The  customary  way  of  obtaining  oxygen  is  to 
put  about  20  grams  of  potassium  chlorate  and  an  equal  amount 
of  manganese  dioxide  in  a  large  test-tube  and  heat  the  mixture 
over  the  bunsen  burner.  The  test-tube  should  be  closed  with 


76  EXPERIMENTAL   GENERAL   SCIENCE 

a  one-hole  stopper  through  which  the  glass  tube  is  thrust.  The 
oxygen  given  off  through  this  tube,  if  conducted  into  a  dish  of 
water,  may  be  seen  bubbling  up  through  it.  By  filling  the  test- 
tube  with  water  and  inverting  it  in  the  dish  of  water  over  the 
rising  bubbles  of  gas,  they  will  displace  the  liquid  in  the  test- 
tube.  Before  being  removed  from  the  water  the  test-tube 
must  be  closed  with  the  finger  or  a  small  sheet  of  glass  to  pre- 
vent the  escape  of  the  gas.  If  a  large  bottle  or  other  recep- 
tacle be  filled  with  the  gas  it  may  also  be  prevented  from  escap- 
ing by  covering  the  mouth  with  a  sheet  of  glass.  Since  all 
gases  are  lighter  than  water,  all  may  be  caught  over  water 
in  the  same  way.  Hydrogen  is  so  much  lighter  than  air  that  it 
may  also  be  caught  over  air  in  an  inverted  test-tube.  Carbon 
dioxide  is  best  prepared  by  pouring  a  little  dilute  hydrochloric 
acid  over  a  few  pieces  of  limestone  or  marble  in  a  test-tube.  It 
may  also  be  obtained  by  heating  baking  soda. 

73.  Carbon  Dioxide. — The  union  of  carbon  with  oxygen 
forms  a  colorless,  odorless,  tasteless  gas  called  carbon  dioxide. 
Since  the  oxygen  it  contains  is  not  in  a  form  that  our  bodies  can 
use  in  respiration,  carbon  dioxide  is  a  suffocating  gas,  but  it  is 
not  poisonous  as  is  frequently  supposed.  It  is  this  gas  that 
gives  the  sparkle  to  wine  and  other  effervescent  drinks  and  the 
pungent  taste  to  soda  water.  Bread,  cake,  and  the  like  are 
made  light  by  bubbles  of  carbon  dioxide  in  the  dough.  Al- 
though carbon  dioxide  does  not  support  ordinary  combustion, 
the  metal  magnesium  will  burn  in  it,  tearing  the  oxygen  from 
the  carbon  for  the  purpose.  When  carbon  dioxide  is  mixed 
with  lime-water,  it  gives  the  latter  a  milky  appearance,  and 
this  liquid  is  commonly  used  as  a  test  for  the  gas.  Carbon 
dioxide  is  slightly  heavier  than  air  and  has  a  tendency  to 
accumulate  in  the  bottom  of  wells,  abandoned  mines,  caves, 
and  similar  places.  People  are  sometimes  suffocated  by 
venturing  into  such  places  without  first  testing  it  for  this  gas. 
Since  fires  will  not  burn  in  carbon  dioxide,  another  test  for 


COMBUSTION  AND   OXIDATION  77 

the  gas  is  a  lighted  candle.  One  should  not  enter  caves,  wells, 
or  cisterns  in  which  a  candle  will  not  burn.  Most  fire  extin- 
guishers are  made  of  substances  which  liberate  a  large  amount 
of  carbon  dioxide  when  necessary.  A  common  form  contains 
a  quantity  of  baking  soda  dissolved  in  water  with  some  means 
of  adding  acid  when  the  extinguisher  is  to  be  used.  The  acid 
combining  with  the  baking  soda  and  water  generates  so  much 
gas  that  the  pressure  forces  both  gas  and  water  out  upon  the 
fire. 


FIG.  26. — Carbon  dioxide  generated  in  test-       FIG.  27. — Bunsen  burner, 
tube  with  limestone  and  dilute  hydrochloric 
acid. 

74.  The  Bunsen  Burner. — One  of  the  most  useful  pieces  of 
apparatus  in  the  chemical  and  physical  laboratory  is  the  bun- 
sen  burner,  which  is  simply  a  device  for  securing  a  hot  flame, 
and  is  based  on  the  fact  that  the  more  thoroughly  oxygen  is 
mixed  with  a  combustible  substance  the  more  rapidly  it  will 
burn.  A  common  form  consists  of  an  upright  tube  connected 
with  the  gas  supply  and  having  an  opening  in  the  base  for  the 
admission  of  air.  When  the  gas  is  turned  on,  its  passage 
through  the  tube  draws  air  in  at  the  base  and  this,  mixing 


78  EXPERIMENTAL   GENERAL   SCIENCE 

with  the  gas,  supplies  the  additional  oxygen  necessary  for  com- 
plete and  rapid  burning,  and  consequently  produces  great  heat. 

Practical  Exercises 

1.  Prepare  a  bottle  of  oxygen  by  some  of  the  methods  suggested. 
What  color  is  oxygen? 


2.  Test  the  gas  with  a  glowing  but  not  blazing  splinter.     Will  oxygen 
burn? 


3.  How  does  oxygen  compare  with  air  as  a  supporter  of  combustion? 


4.  Untwist  the  strands  at  one  end  of  a  piece  of  picture  wire.  Wrap 
one  strand  about  the  head  of  a  match.  Light  the  match  and  when 
burning  well  lower  into  a  bottle  of  oxygen.  Explain  the  result. 


5.  Prepare   carbon   dioxide   as  directed  and  test  it  with  a  lighted 
splinter.     Will  carbon  dioxide  burn? 


6.  Will  carbon  dioxide  support  combustion? 


7.  Catch  another  test-tube  of  the  gas  and  pour  into  it  about  10  cubic 
centimeters  of  lime-water.  Shake  it  well  and  note  the  result.  This  is 
an  infallible  test  for  carbon  dioxide. 


8.  Put  about  5  cubic  centimeters  of  lime-water  into  a  clean  test-tube 
and  try  to  pour  a  test-tube  of  carbon  dioxide  into  it.  Which  do  you 
conclude  is  heavier,  carbon  dioxide  or  ordinary  air? 


9.  Light  a  candle  end  and  place  it  in  the  bottom  of  a  clean,  dry  fruit 
jar  or  wide-mouthed  bottle.  Cover  the  mouth  of  the  jar  with  a  sheet  of 
glass  or  cardboard  and  let  it  stand  for  a  few  minutes.  What  change 
takes  place  in  the  candle  flame.  Why? 


COMBUSTION   AND    OXIDATION  79 

10.  Keeping  the  jar  upright,  remove  the  candle  and  pour  into  the  jar 
about  10  cubic  centimeters  of  lime-water.  Shake  it  and  note  the  result. 
With  what  substance  in  the  candle  has  the  oxygen  of  the  air  united? 


11.  Place  the  candle  end  on  the  table,  light  it  and  hold  the  mouth  of  a 
cold  dry  bottle  over  the  flame.  What  soon  covers  the  inside  of  the 
bottle? 


12.  Press  a  white  card  down  on  the  candle  flame  in  such  a  way  that  the 
tip  of  the  flame  is  flattened  out  against  the  card.     When  the  card  begins 
to  char,  remove  it  and  examine.     Where  was  the  flame  the  hottest? 
Why? 

13.  Press  a  clean  white  dish  or  sheet  of  metal  down  on  the  candle 
flame  for  a  few  seconds.     What  chemical  element  is  deposited  on  the 
object? 

14.  Why  was  it  not  burned? 


16.  Light  a  candle  and  after  it  has  been  burning  a  few  seconds,  blow 
it  out  and  immediately  hold  a  lighted  match  about  an  inch  above  the 
wick  in  the  smoky  substance  rising  from  it.  What  inference  do  you  make 
as  to  whether  the  burning  substance  is  a  solid,  a  liquid,  or  a  gas? 


16.  Hydrogen  and  oxygen  unite  with  much  heat  to  form  water.     Can 
you  tell  why  such  a  flame  never  smokes? 

17.  Blow  your  breath  through  a  straw  or  glass  tube  into  half  a  test- 
tube  of  lime-water.     What  chemical  substance  in  the  breath  does  this 
show? 


18.  In  the  process  of  making  wood  alcohol,  the  wood  is  placed  in 
an  air-tight  cylinder  and  heated  very  hot.  When  the  cylinder  is  opened 
the  wood,  instead  of  being  burned  up,  is  found  to  have  become  charcoal. 
Explain. 


80  EXPERIMENTAL   GENERAL  SCIENCE 

19.  The  filament  in  certain  electric  light  bulbs  is  made  of  carbon. 
Why  is  it  not  consumed  when  the  electricity  is  turned  on? 


20.  Dissolve  a  piece  of  phosphorus,  half  the  size  of  a  pea,  in  about  3 
cubic  centimeters  of  carbon  disulphide.     (Do  not  touch  the  phosphorus 
with  the  hands.)     Support  a  piece  of  blotting  paper  or  filter  paper  on  a 
ring  stand  and  pour  the  solution  over  it.     What  happens  when  the  liquid 
evaporates,  leaving  the  phosphorus? 

21.  What    form    of    combustion    is    illustrated    by    the    foregoing 
experiment? 

22.  Is  the  kindling  temperature  of  wood  higher  or  lower  than  the 
temperature  of  the  school-room? 

23.  Why  do  gasoline  engines  require  that  a  certain  amount  of  air  be 
admitted  to  the  cylinders  with  the  gasoline? 

24.  Why  cannot  sodium  be  preserved  under  water? 

25.  Examine  the  bunsen  burner  and  find  the  hole  at  the  base  for  the 
admission  of  air.     Close  this  opening,  turn  on  the  gas  and  light  it. 
What  color  is  the  flame?    Why? 

26.  Admit  air  to  the  burner.     What  effect  has  this  on  the  color  of  the 
flame?    Why? 

27.  Press  a  sheet  of  metal  down  upon  the  orange  flame  for  a  few 
seconds.     What  is  deposited  on  the  metal? 

28.  Make  the  same  experiment  with  the  blue  flame.     How  do  you 
account  for  the  difference. 


29.  Why  does  a  candle  or  lamp  smoke  when  not  well  supplied  with 
air? 


COMBUSTION  AND   OXIDATION  81 

30.  Large  oil  lamps  and  oil  heaters  have  a  circular  burner  with  an 
opening  in  the  center  through  which  air  circulates.  Of  what  advantage 
is  this? 


31.  Why  does  blowing  or  fanning  a  fire  make  it  burn  faster? 


32.  Try  heating  a  glass  rod  or  piece  of  wire,  first  in  the  tip  of  the  blue 
flame  and  then  in  the  orange  flame.     Which  is  the  hotter? 


33.  Does  the 'hotter  flame  use  more  gas?    If  not,  how  do  you  account 
for  the  heat? 


FIG.  28. — Effect  of  wire  gauze  on  flame.     (Jones.) 

34.  All  gas  ranges  are  constructed  on  the  principle  of  the  bunsen 
burner.  Examine  such  a  range  and  locate  the  opening  through  which 
air  is  admitted  to  the  burner. 


35.  Should  the  flame  of  the  gas  range  be  blue,  or  orange-colored? 

36.  Light  the  bunsen  burner  and  press  a  piece  of  wire  gauze  down  on 
the  flame.    Does  the  flame  pass  through  the  gauze? 


37.  Place  a  piece  of  wire  gauze  on  the  bunsen  burner  in  such  a  way 
that  the  gas  will  rise  through  it.  Turn  on  and  light  the  gas  above  the 
gauze.  Then  slowly  lift  the  gauze  up  from  the  burner.  Does  the  flame 
pass  through  the  gauze? 


82  EXPERIMENTAL   GENERAL   SCIENCE 

38.  Explain  why  it  is  customary  to  place  a  piece  of  wire  gauze  under 
beakers,  florence  flasks,  and  the  like,  when  heating  them  over  a  bunsen 
burner. 


39.  Why  does  a  blanket  smother  a  fire? 

40.  For  putting  out  a  fire  in  oil,  which  is  better,  water  or  sand?     Why ' 

41.  Would  flour  be  of  use  in  putting  out  an  oil  fire? 


CHAPTER  XIII 
CONDUCTION  AND  RADIATION 

76.  Transference  of  Heat. — Whenever  a  body  is  placed  in 
surroundings  cooler  or  warmer  than  itself,  a  transference  of 
heat  at  once  begins,  the  warmer  object  giving  up  its  heat  to 
the  cooler  ones  until  all  are  of  the  same  temperature.  Ice 
placed  in  the  refrigerator  begins  at  once  to  melt,  withdrawing 
the  heat  for  this  change  of  state  from  the  contents  of  the  re- 
frigerator and  so  cooling  it.  -  On  the  other  hand,  a  hot  piece 
of  iron  brought  into  a  room  will  warm  it  by  giving  off  its  sur- 
plus heat.  After  a  body  and  its  surroundings  have  reached 
a  uniform  temperature,  however,  no  further  transference  of 
heat  takes  place  until  some  new  difference  in  temperature 
causes  it  to  begin  again.  Heat,  though  a  form  of  energy  and 
not  of  matter,  seems  thus  to  act  like  water  and  other  liquids, 
flowing  from  a  higher  to  a  lower  level  until  an  exact  balance 
is  reached.  Such  a  balance,  however,  is  seldom  long  undis- 
turbed. The  earth  daily  receives  an  immense  amount  of  heat 
upon  that  part  of  its  surface  which  is  turned  toward  the  sun 
and  as  regularly  loses  it  from  the  parts  upon  which  the  sun 
does  not  shine.  Combustion  and  oxidation  add  a  share  to 
the  change  of  temperature  which  matter  undergoes,  hot  and 
cold  winds  make  new  distributions  of  heat  necessary,  and 
various  other  causes  contribute  to  the  almost  ceaseless  changes 
that  take  place  in  the  temperature  of  matter. 

76.  Conduction. — One  important  way  in  which  a  body  may 
lose  heat  to,  or  absorb  heat  from,  another  is  by  actual  contact, 
as  when  water  is  boiled  by  being  placed  on  a  hot  stove.  The 
heat,  that  is,  the  motion  of  the  molecules,  is  conducted  directly 

83 


84  EXPEEIMENTAL  GENERAL  SCIENCE 

from  the  warmer  body  to  the  cooler  one.  Heat  also  travels 
readily  from  molecule  to  molecule  through  a  substance.  A 
piece  of  metal  left  with  one  end  in  the  fire  will  soon  become 
hot  at  the  other  by  conduction.  Recalling  the  molecular 
structure  of  matter,  one  easily  understands  that  solids  with 
their  molecules  close  together  must  in  general  be  the  best  con- 
ductors of  heat  and  gases  the  poorest.  All  solids,  however,  do 
not  conduct  heat  equally  well.  The  metals,  especially  silver 
and  copper,  are  among  the  best  conductors,  while  wood  and 
stone  are  much  poorer. 

77.  Radiation. — The  second  way  in  which  the  molecular 
motion  of  a  body  may  be  given  to  another  is  by  rays  sent  out 
from  it  just  as  heat  rays  are  sent  out  from  the  sun.     When  we 
approach  the  fire,  the  radiation  from  it  makes  us  aware  that 
it  is  giving  out  heat  before  we  actually  come  into  contact  with 
it.     As  we  have  discovered,  the  heat  energy  radiated  from  the 
sun  passes  unchanged  through  most  transparent  substances, 
and  the  heat  energy  from  very  hot  bodies  on  the  earth  act  in 
the  same  way,  but  the  longer  heat  rays  given  off  by  cooler 
bodies  pass  more  slowly  through  even  transparent  substances. 
The  earth  receives  and  loses  heat  entirely  by  radiation. 

78.  Insulators. — Substances  which  offer  resistance  to  the 
passage  of  heat  through  them  are  called  insulators.    A  poor 
conductor,   therefore,   is   a  good  insulator,   and  vice  versa. 
Wood,  paper,  leather,  cotton,  wool,  feathers,  sand,  and  similar 
substances  make  good  insulators.     Porous  materials  always 
make  especially  good  insulators  because  of  the  number  of 
small  air  spaces  which  they  contain.     Air  is  like  other  gases 
in  being  a  poor  conductor,  and,  when  stationary,  as  it  is  in 
these  small  spaces,  very  greatly  retards  the  passage  of  heat 
across  it.     When  air  can  move  about,  however,  it  readily 
carries  away  heat  from  a  body. 

79.  Absorption  and  Reflection. — It  has  been  proved  by 
numerous  experiments  that  the  nature  of  a  surface  and  even 


CONDUCTION  AND.   EADIATION  85 

its  color  has  an  important  bearing  upon  the  rapidity  with 
which  it  absorbs  or  radiates  heat.  A  black  object  usually 
warms  more  readily  than  a  lighter  one  because  the  latter  re- 
flects many  of  both  the  light  and  heat  rays,  while  black  objects 
absorb  them  and  so  increase  in  temperature.  It  is  for  this 
reason  that  light-colored  clothing  is  worn  in  summer  and  dark- 
colored  clothing  in  winter.  Dark  soils  are  usually  early  soils 
because  they  absorb  heat  so  readily  in  early  spring.  As  might 
be  inferred  from  the  fact  that  heat,  like  light,  can  be  reflected, 
smooth  surfaces  reflect  much  heat  and  warm  more  slowly  than 
rough  surfaces.  When  a  body  with  a  smooth  surface  is  once 
warmed,  however,  it  cannot  radiate  its  heat  as  rapidly  as  a 
rough  one.  In  general,  then,  good  reflectors  are  poor  radiators 
and  poor  reflectors  are  good  radiators. 

80.  Distribution  of  Heat. — All  parts  of  the  earth  receive 
the  same  number  of  hours  of  sunlight  annually,  but  this  by 
no  means  indicates  that  they  are  all  equally  warmed.  One 
reason  for  the  difference  in  the  temperature  is  the  unequal 
periods  of  time  during  which  different  regions  are  heated  or 
cooled.  In  the  tropics,  there  are  twelve  hours  of  sunlight  and 
twelve  hours  of  darkness  throughout  the  year.  In  the  Arctic 
or  Antarctic  regions,  there  is  a  six  month's  period  of  daylight 
and  an  equal  period  of  darkness  annually.  In  the  temperate 
zone,  the  length  of  the  day  and  night  varies  between  these 
extremes.  At  mid-summer  in  the  Northern  States,  the  day 
is  about  fifteen  hours  long  and  the  night  correspondingly 
shorter,  and  in  winter  these  conditions  are  reversed.  This 
difference  in  the  length  of  daylight  over  different  parts  of  the 
earth  is  well  known  to  be  due  to  the  angle  at  which  the  earth's 
axis  is  maintained  with  reference  to  the  sun.  In  summer  it  is 
inclined  toward  the  sun  and  thus  the  season  of  daylight  is 
lengthened.  In  winter  it  is  turned  away  and  the  season  of 
darkness  is  increased.  It  is  not  the  length  of  the  period  of 
daylight  alone,  however,  which  determines  the  temperature  of 


86  EXPERIMENTAL   GENERAL   SCIENCE 

a  place.  The  angle  at  which  the  sun's  rays  are  received  have 
an  important  bearing  on  the  subject.  The  amount  of  heat 
sent  us  by  the  sun  does  not  change  materially  from  day  to 
day.  When  the  sun  is  directly  overhead,  the  heat  energy 
falling  on  each  square  centimeter  is  about  1%  calories  a  min- 
ute, summer  or  winter.  Owing  to  the  shape  of  the  earth,  how- 
ever, and  the  direction  of  its  axis,  that  part  of  its  surface  out- 
side of  the  tropics  always  receives  the  rays  in  a  more  or  less 
slanting  direction,  and  the  heat  and  light  are  in  consequence 
distributed  over  a  greater  area.  Nevertheless,  at  the  time  of 


FIG.  29. — Distribution  of  heat  rays  at  morning  and  night. 

the  summer  solstice  when  the  longest  period  of  daylight  occurs 
in  the  Northern  Hemisphere,  the  north  pole  receives  much 
more  heat  than  the  equator.  Owing  to  the  evaporation  of  the 
ice  and  snow,  however,  it  is  not  correspondingly  heated.  The 
region  of  greatest  heating  at  that  time  is  near  the  latitude  of 
Chicago  and  Buffalo  (§152). 

81.  The  Lag  in  Temperature. — The  longest  day  in  the 
Northern  Hemisphere  is  in  June  and  the  shortest  is  in  Decem- 
ber, but  June  is  seldom  if  ever  our  hottest  month  or  December 
the  coldest.  Moreover,  since  the  sun  is  more  nearly  overhead 
at  noon  than  at  any  other  time,  noon  should  be  the  hottest  part 


CONDUCTION   AND    RADIATION  87 

of  the  day,  and  yet  this  period  usually  comes  one  or  two  hours 
later.  Morning  also  is  likely  to  be  cooler  than  midnight.  The 
reason  for  such  lags  in  temperature  may  be  explained  by  what 
we  know  of  the  phenomena  of  radiation.  When  the  days  are 
long  and  the  nights  are  short,  as  in  summer,  the  period  of  daily 
heating  is  much  greater  than  the  period  in  which  the  heat  can 
be  radiated.  Consequently,  the  earth  accumulates  heat.  In 
winter  we  daily  radiate  more  heat  than  we  receive  and  continue 
to  lose  heat  until  the  lengthening  days  of  late  winter  bring  us 
enough  extra  heat  to  balance  the  daily  outgo.  The  increased 
temperature  after  mid-day  may  be  explained  in  the  same  way. 
It  is  now  easy  to  understand  why  regions  near  the  equator 
have  a  less  variable  temperature  than  those  near  the  poles. 
Their  periods  of  heating  and  cooling  are  almost  exactly 
balanced  throughout  the  year. 

82.  The  Effects  of  Gas  and  Dust  on  Radiation.— Dust  and 
smoke  in  the  air  intercept  the  radiation  from  the  earth  and  act 
like  a  blanket  to  keep  in  the  heat.     This  explains  why  the  city 
is  warmer  than  the  country  during  our  heated  season.     The 
carbon  dioxide  and  water  vapor  in  the  air,  however,  are  fully  as 
important  in  this  connection.     Though  they  allow  the  heat 
energy  from  the  sun  to  pass  to  the  earth,  they  readily  absorb 
the  long  heat  rays  and  become  warm  themselves.     In  fact 
if  it  were  not  for  the  presence  of  these  two  gases  in  the  atmos- 
phere, the  earth  would  lose  heat  so  rapidly  at  night,  even  in 
summer,  as  to  approach  dangerously  near  the  freezing  point. 
The  variations  of  temperature  in  deserts,  where  the  air  is  dry, 
are  frequently  much  greater  than  in  places  where  there  is  more 
moisture  in  the  air.     Many  orchards  are  now  equipped  with 
means  for  making  a  smudge  to  protect  the  trees  from  unseason- 
able frosts.     A  fog  over  the  orchard  may  have  the  same  effect. 

83.  Heat  and  Living  Things. — A  certain  amount  of  heat  is 
necessary  to  the  existence  of  all  living  things.     Since  most  of 
their  life  processes  are  due  to  chemical  reactions,  much  of  this 


88 


EXPERIMENTAL   GENERAL   SCIENCE 


heat  may  come  from  the  organisms  themselves  Even  plants 
generate  a  small  amount  of  heat  (§182).  Respiration,  as  we 
have  seen,  is  really  a  slow  burning  which  occurs  in  both  animals 
and  plants.  The  lower  animals  usually  have  a  temperature 
not  very  different  from  their  surroundings,  but  birds  and  mam- 
mals have  a  temperature  higher  than  that  which  ordinarily 
prevails,  and  this  temperature  is  maintained  nearly  uniform 
whether  the  surroundings  be  hot  or  cold.  In  health,  our  own 
bodies  have  a  temperature  of  about  98.6°F.;  and  if  anything 
occurs  to  prevent  the  loss  of  the  excess  heat  produced,  we  soon 
have  a  fever.  The  sense  by  which  we  judge  the  temperature  of 
an  object  is  very  easily  deceived.  A  piece  of  iron  will  feel 
colder  than  a  piece  of  wood  on  a  cold  morning,  but  the  ther- 
mometer proves  it  to  be  of  the  same  temperature.  On  a  hot 
day  iron  will  feel  hotter  than  wood.  The  explanation  of  this  is 
that  when  we  are  losing  heat  rapidly  we  feel  chilly,  and  when 
we  are  gaining  heat  rapidly  we  feel  warm.  Metal  being  a 
good  conductor  of  heat,  therefore,  is  apparently,  but  not 
really,  colder  or  hotter  than  wood  (§45). 

84.  Uses  of  Radiation  and  Conduction. — Many  familiar 
operations  make  use  of  the  principles  of  radiation  and  con- 
duction. In  the  ice  cream  freezer 
the  material  to  be  frozen  is  put 
into  a  metal  vessel  surrounded  by 
salt  and  ice.  The  metal,  being  a  good 
conductor,  rapidly  transfers  the  heat 
from  the  cream  to  the  melting  ice. 
The  outside  of  the  freezer  is  usually 
made  of  wood,  a  poor  conductor, 
which  prevents  the  ice  from  being 
melted  by  the  heat  from  outside.  In 
FIG.  30.— A  fireiess  cooker,  the  fireless  cooker,  the  heated  food  is 
(Ahrens,HarieV  and  Burns.)  surrounded  by  a  layer  of  hay,  cork 
dust,  excelsior,  or  other  material  in  which  are  many  small 


CONDUCTION   AND   RADIATION 


CLASS  NECK 


METAL  NECK 


spaces  containing  air.  Since  heat  crosses  stationary  air  very 
slowly,  most  of  it  remains  in  the  food  for  a  long  time  and  so 
cooks  it.  If  the  tireless  cooker  be 
first  cooled,  it  will  then  keep  cold 
foods  cold  equally  well.  In  this 
case  the  stationary  air  spaces  pre- 
vent the  heat  from  getting  in  and 
warming  the  food.  The  thermos 
bottles  which  so  mysteriously  retain 
the  temperature  of  anything  put 
into  them,  hot  or  cold,  consist  of 
double- walled  vessels  with  a  vacuum 
between  the  walls.  Heat  passes 
through  a  vacuum  even  more 
slowly  than  it  passes  through  air, 
and  the  interior  is  prevented  from 
either  absorbing  or  radiating  heat 
rapidly.  The  warm-blooded 
animals  are  kept  warm  in  winter 
by  the  stationary  air  in  their  fur  or 
feathers.  When  the  weather  is  ex- 
tremely cold,  both  birds  and  mam- 
mals are  accustomed  to  fluff  up 
their  coats  and  thus  include  more 
air  as  a  greater  protection  from 
the  cold.  The  same  principle  is 
made  use  of  in  winter  when  we 
cover  the  ground  about  bulbs, 
half-hardy  plants,  and 
planted  shrubbery,  with  a  mulch  of 
leaves,  straw,  or  stable  manure.  While  the  mulch  does  not 
entirely  prevent  the  earth  from  freezing,  the  air  spaces  it  con- 
tains protect  the  specimens  from  the  sudden  changes  in  tem- 
perature which  are  more  trying  to  them  than  steady  cold. 


newly  !j,ot,tle- 

*    Turton.) 


FIG.  31. — Section  of  a  Thermos 
(Tower,  Smith     and 


90  EXPERIMENTAL   GENERAL   SCIENCE 


Practical  Exercises 

1.  When   a   hot   flat-iron  cools  in  ironing,  does  it  lose  its  heat  by 
conduction  or  by  radiation? 


2.  Savages  used  to  boil  water  by  putting  hot  stones  in  it.     Was  the 
water  warmed  by  conduction  or  by  radiation? 

3.  By  what  method  does  a  coal  stove  warm  a  room? 

4.  Is  a  steam-heated  flat  warmed  by  conduction  or  by  radiation? 

5.  Which  is  a  better  conductor  of  heat,  copper  or  iron?     (Find  out 
by  heating  six-inch  sections  of  copper  and  iron  wire  in  the  bunsen 
burner.) 

6.  Would  a  flat-iron  be  as  useful  if  made  of  copper? 

7.  Why    are    steam  pipes  usually  covered  with  asbestos  or  other 
porous  material? 


8.  Why  does  frost  remain  longer  on  the  boards  of  a  walk  than  it  does 
on  the  heads  of  the  nails  in  the  boards? 


9.  Fill  a  test-tube  with  water  and  by  means  of  a  bunsen  burner  apply 
heat  near  the  open  end.  When  the  water  begins  to  boil  there,  feel  of  the 
bottom  of  the  tube.  What  do  you  learn  from  this  experiment  as  to 
whether  or  not  liquids  are  good  conductors  of  heat? 


10.  Why  can  one  touch  a  hot  iron  with  a  wet  finger  and  not  be 
burned?     (Note  that  the  moisture  turns  to  gas.)     (§78.) 

11.  Why  will  a  flask  filled  with  hot  water  cool  off  more  slowly  if 
wrapped  with  cotton  batting  ? 


CONDUCTION   AND    KADIATION  91 

12.  Why  is  loosely  woven  clothing  warmer  in  winter  than  more  closely 
woven  fabrics? 


13.  Why  may  loosely  woven  clothing  be  cooler  in  summer  than  more 
closely  woven  fabrics? 


14.  Which  is  warmer,  close-fitting  or  loose-fitting  underwear?     Why? 

15.  How  do  double  windows  keep  the  house  warm  in  winter? 

16.  Do  we  warm  our  clothes,  or  do  our  clothes  warm  us? 

17.  Ice-houses  and  refrigerators  have  double  walls  between  which  is 
a  packing  of  sawdust,  charcoal,  cork-dust,  or  the  like.     How  does  this 
help  to  keep  the  ice  from  melting? 


18.  Wrapping  the  ice  in  the  refrigerator  with  newspaper  will  retard 
the  melting  of  the  ice.  How  does  this  affect  the  temperature  of  the 
refrigerator? 


19.  Ordinary  electric  light  bulbs  have  no  air  in  them.  Certain  others 
are  filled  with  nitrogen  gas.  Why  do  the  bulbs  of  the  latter  get  so  much 
hotter? 


20.  Why  does  a  crack  in  the  outside  of  a  thermos  bottle  impair  its 
usefulness? 


21.  Snow  is  called  "the  poor  man's  manure"  because  it  protects  the 
crops  left  out  over  winter  from  sudden  changes  of  temperature.  How 
does  it  do  this? 


22.  The  outer  bark  of  trees  consists  of  many  dead  cells  containing  air. 
How  does  this  protect  the  trees  from  sudden  changes  in  temperature? 


92  EXPERIMENTAL   GENERAL   SCIENCE 

23.  Which  makes  a  better  holder  for  flat-irons  and  cooking  utensils, 
a  cotton  or  a  woolen  cloth?     Why? 


24.  Why  are  the  handles  of  tea  kettles,  coffee  pots,  and  the  like  usually 
made  of  wood  instead  of  metal? 


25.  In  which  could  you  heat  water  more  quickly,  a  tin  or  a  china 
cup? 


26.  Frozen  mercury  thrown  into  water  soon  melts,  but  the  water 
becomes  solid.     How  do  you  explain  this? 


27.  A  kettle  of  liquid  air  will  boil  if  set  on  a  cake  of  ice.     Where  does 
it  get  the  heat  for  this? 


28.  In  canning,  why  do  people  often  put  a  silver  spoon  in  the  jar 
before  putting  in  the  hot  fruit? 


29.  On  which  would  a  kettle  of  hot  water  cool  more  quickly,  iron  or 
wood?    Why? 


30.  Should  a  coffee  pot  have  a  smooth  or  a  rough  surface?    Why? 


31.  In  the  air-cooled  gas  engine,  the  cylinders  have  many  projections 
on  them.     Why? 


32.  Which  should  be  warmer  in  the  sunshine,  a  polished  shoe  or 
dusty  one? 


33.  Why  do  people  wear  white  in  summer  and  black  in  winter? 

34.  A  black  soil  is  regarded  as  a  warm  soil.     Why? 


CONDUCTION  AND   RADIATION  93 

35.  Which  is  best  for  an  early  garden,  a  level  field  or  one  sloping  toward 
the  south?    Why? 


36.  Why  does  a  black  object  melt  into  snow  or  ice  faster  than  a 
lighter-colored  one? 

37.  In  regions  where  there  is  much  sunlight,  water  for  domestic  pur- 
poses is  sometimes  heated  by  being  passed  through  a  coil  of  pipes  exposed 
to  the  sun's  rays.     The  pipes  are  painted  black.     Why? 

38.  The  pipes  mentioned  above  are  usually  enclosed  in  a  box  with  the 
side  toward  the  sun  made  of  glass.     How  does  this  increase  its  efficiency? 

39.  Would  it  be  of  any  use  to  surround  the  box  with  a  layer  of  straw, 
excelsior  or  sawdust?     Explain. 

40.  How  does  spreading  cloth  or  paper  over  plants  protect  them 
from  the  frosts  of  early  autumn? 

41.  When  dew  gathers  on  plants,  how  does  it  prevent  further  radiation 
of  their  heat  (§76)? 

42.  Why  does  no  dew  form  on  cloudy  nights?     (A  lowering  of  the  tem- 
perature is  necessary  for  the  formation  of  dew.)     (§82.) 

43.  Why  does  the  floor  feel  colder  to  the  bare  feet  than  a  rug  or  carpet? 

44.  The  Sahara  desert  is  in  the  tropics  and  yet  the  air  there  may  become 
so  cold  at  night  as  to  freeze  water.     Why? 

46.  Why  do  we  receive  less  heat  and  light  from  the  sun  at  morning  and 
evening  than  at  midday? 

46.  In  winter  the  sun  is  some  millions  of  miles  nearer  the  earth  than 
it  is  in  summer  and  yet  it  is  hotter  in  summer.     Explain. 


94  EXPERIMENTAL   GENERAL   SCIENCE 

47.  Why  is  the  air  in  lowlands  and  valleys  likely  to  be  warmer  than 
that  on  mountain  tops? 


48.  On  high  mountains,  explorers  are  often  badly  sunburned  though 
they  may  suffer  from  the  cold.     Explain. 


CHAPTER  XIV 


CONVECTION 

85.  Convection  Currents.  —  When  air  is  heated,  either  by 
conduction  or  radiation,  it  expands,  becomes  less  dense,  and  is 
pushed  upward  by  the  surrounding  cooler  air  near  it.     This 
upward  current  of  air  is  called  a  convection  current.     It  really  is 
but  part  of  a  circuit  of  larger  or  smaller  diameter,  for  if  the 
current  of  air  rises  in  one  place  a  similar  current  must  descend 
in  another  to  take  the  place  of  the 

air  that  has  risen.     A  convection  cir- 

cuit of  this  kind  is  always  caused  by 

a  difference  in  the  temperature  of 

the  air.     A  cake  of  ice  which  cools 

the  air  and  makes  it  heavier  will 

cause  a  convection  current  just  as 

feadily  as  heat  will,  although  in  this 

case  the  initial  movement  is  down- 

ward instead  of  upward.     Convec- 

tion is  sometimes  described  as  a  third 

way  in  which  objects  lose  heat,  but  it 

is  very  evident  that  no  new  principle 

is  involved,  and  that  the  heating  or  cooling  of  a  body  exposed 

to  the  air  movement  is  primarily  due  to  radiation  or  conducton. 

Convection  currents  may  also  be  caused  by  variations  in  the 

amount  of  moisture  in  the  air.     Moist  air  is  lighter  than  dry 

air  and  of  course  has  a  tendency  to  rise  above  it. 

86.  Winds.  —  Probably  the  most  noticeable  convection  cur- 
rents are  those  which  occur  as  the  result  of  the  unequal  heating 
of  the  air  over  adjacent  regions.     When  this  occurs,  a  circuit  is 

95 


FIO.  32.  —  Convection  cur- 
in    air-     <-Black    and 


96 


EXPERIMENTAL  GENERAL   SCIENCE 


set  up  which  may  be  limited  to  a  portion  of  a  township,  a 
county,  or  extend  over  one  or  more  States.  The  currents 
which  flow  along  the  ground  from  one  region  to  another  are 
familiarly  known  as  winds.  Since  changes  in  the  position  of 
the  air  are  due  to  differences  in  its  density,  it  is  easy  to  realize 
that  the  greater  the  difference  between  two  regions  the  greater 
will  be  the  speed  of  the  winds  produced.  Most  interesting 
illustrations  of  this  may  be  observed  near  large  bodies  of  water. 
During  the  hours  of  sunshine,  the  land  warms  more  rapidly 


FIG.  33. — Convection  currents  in  a  room.     (Tower,  Smith  and  Turton.} 

than  the  water,  and  early  in  the  day  the  breeze  begins  to  blow 
inland.  At  night  the  land  loses  heat  much  more  rapidly  than 
the  water  and  soon  is  cooler.  Then  the  breeze  from  the  land 
to  the  water  sets  in.  In  regions  where  the  land  slopes  rapidly 
toward  the  water  and  also  receives  the  direct  rays  of  the  sun, 
the  effects  are  especially  noticeable.  The  winds  which  blow 
toward  the  great  storms  or  cyclones  that  move  across  the 
country  from  west  to  east  at  intervals  of  a  few  days  during 
most  of  the  year  do  not  blow  straight  toward  the  center  of 
the  storm  area.  Owing  to  the  rotation  of  the  earth  they 


CONVECTION 


97 


acquire  a  somewhat  circular  course  and  blow  around  the 
storm  center  or  low.  In  the  northern  hemisphere  the  direction 
of  the  winds  about  a  low  is  the  reverse  of  the  direction 
in  which  the  hands  of  a  clock  move,  or  counter  clockwise. 
South  of  the  equator  the  winds  blow  clockwise  about  a  low. 
The  periods  of  fair  weather  between  two  lows  are  called 
anticyclones.  On  a  weather  map  such  periods  are  marked 
highs. 


FIG.  34. — Heating  and  ventilating  by  means  of  a  hot-air  furnace.     (Tower, 

Smith  and  Turton.) 

87.  Convection  in  Liquids. — Though  convection  currents  in 
liquids  may  be  less  noticeable,  they  are  nevertheless  as  inevi- 
table when  a  change  in  density  occurs.  Proof  of  this  may  be 
seen  by  filling  a  florence  flask  with  water  and  gently  heating  it 
after  dropping  into  the  flask  a  few  grains  of  potassium  per- 
manganate or  other  coloring  matter  to  make  the  currents 
visible.  Our  systems  of  hot-water  heating  depend  upon  a 
convection  circuit  in  which  the  water  is  heated  in  a  boiler  and, 
becoming  less  dense,  rises  in  the  pipes  to  the  rooms  that  are 

7 


98  EXPERIMENTAL    GENERAL   SCIENCE 

to  be  heated.  As  it  gives  off  its  heat  its  density  becomes 
greater  and  it  finally  runs  back  to  the  boiler  where  it  is  reheated 
and  goes  on  its  rounds  again.  Probably  the  greatest  convection 
circuits  of  which  we  have  any  knowledge  are  such  ocean  cur- 
rents as  the  Gulf  Stream  and  Japan  Current  which,  heated 
by  the  sun  near  the  equator,  flow  away  above  the  colder,  heav- 
ier water  of  the  ocean  and,  after  giving  up  their  heat  to  more 
northern  regions,  settle  down  and  slowly  return  to  the  equator. 
88.  Convection  and  Frost. — When  the  air  cools  at  night,  it 
begins  to  settle  down  into  the  hollows,  pushing  out  the  warmer 
and  lighter  air  which  flows  upward  along  the  ground.  For 
this  reason  the  hillsides  often  escape  frost  which  injures  plants 
in  the  valley.  When  the  conformation  of  a  country  is  suitable, 
the  cold  air  may  flow  out  of  a  valley  like  an  invisible  river. 
Such  regions  are  especially  adapted  to  fruit  growing  since  they 
are  not  subject  to  such  great  danger  from  frost.  When  the 
wind  blows,  the  moving  air  prevents  the  cooler  air  from  settling 
in  one  place  and  so  protects  from  frost. 

Practical  Exercises 

1.  Cut  two  holes  about  an  inch  square  and  several  inches  apart  in 
the  cover  of  a  shallow  box,  such  as  a  cigar  box,  and  over  each  hole  set 
a  lamp  chimney.     Below  one  of  the  openings  place  a  lighted  candle  end. 
Light  a  piece  of  touch  paper,  or  anything  else  that  will  make  consider- 
able smoke,  and  hold  it  first  over  one  chimney  and  then  over  the  other. 
Account  for  the  direction  of  the  air  current  in  each  chimney. 

2.  Why  are  refrigerators  usually  built  with  the  space  for  ice  at  the 
top? 


3.  Which  of  our  systems  of  heating  makes  use  of  convection  currents 
in  the  air? 


4.  Would  a  hot-air  furnace  warm  the  house  as  well  if  placed  in  the 
attic  instead  of  in  the  basement?     Why? 


CONVECTION  99 

6.  When  the  sun  shines  on  a  section  of  country,  what  effect  is  it  likely 
to  have  on  the  movement  of  the  air  there? 


6.  Do  you  infer  that  the  wind  blows  from  a  single  direction  or  from 
all  directions  toward  a  column  of  rising  air? 


7.  When  the  wind  blows  from  the  north,  in  what  direction  is  the 
nearest  column  of  rising  air? 

8.  Where  is  it  when  the  wind  blows  from  the  east? 


9.  How  do  you  explain  the  statement  that  the  Gulf  States  help  to 
warm  Chicago? 


10.  On  a  weather  map  the  areas  marked  "High"  are  regions  of  heavy 
air  and  those  marked  "  Low  "  are  regions  of  lighter  air.  In  what  direction 
should  the  air  near  the  ground  move,  from  a  high  to  the  nearest  low  or  the 
reverse? 


11.  In  what  direction  should  the  elevated  currents  connecting  a  high 
and  a  low  flow? 


12.  Why  does  blowing  a  hot  liquid  cool  it? 

13.  On  a  cold  day,  why  does  it  seem  so  much  colder  in  the  wind  than 
in  a  sheltered  situation  (§83)? 

14.  How  does  an  open  fireplace  ventilate  a  room? 

16.  Which  would  be  more  effective  in  ventilating  a  room,  opening  a 
window  at  the  top  or  bottom,  or  opening  it  at  the  top  and  bottom? 
Why? 

16.  Why  does  not  the  carbon  dioxide  produced  by  a  flame  extinguish  it? 


100  EXPERIMENTAL   GENERAL   SCIENCE 

17.j[How  does  the  chimney  keep  a  lamp  from  smoking? 

18.  In  a  hot-water  heating  system  which  pipes  do  you  infer  are  lower, 
those  which  carry  the  water  from  the  heater  or  those  which  bring  it 
back?    Why? 

19.  The  bottom  of  the  ocean,  even  in  the  tropics,  is  known  to  have  a 
temperature  only  a  few  degrees  above  freezing.     How  do  you  account 
for  this? 


20.  In  what  general  direction  do  you  infer  the  water  moves  at  the 
bottom  of  the  ocean? 


21.  When  a  fire  is  lighted  out  of  doors,  why  do  the  sparks  fly  upward 
as  soon  as  it  is  burning  well? 

22.  Why  do  factories  which  burn  coal  secure  a  better  draught  by  the 
use  of  tall  chimneys? 

23.  When  the  fire  is  first  lighted  the  stove  may  smoke.     Why? 


CHAPTER  XV 
EVAPORATION 

89.  Conditions  Affecting  Evaporation. — Evaporation  is  the 
name  given  to  that  change  of  state  in  which  a  liquid  assumes 
the  gaseous  form.  Liquids  will  evaporate  at  any  temperature 
but,  since  heat  is  always  absorbed  in  the  process,  the  warmer 
the  substance  is  made  the  faster  will  evaporation  take  place. 
When  a  substance  evaporates  without  the  special  application 
of  heat  we  assume  that  the  heat  necessary  is  derived  from  sur- 
rounding objects,  and  this  proves  to  be  the  case,  for  evapo- 
rating liquids  are  always  somewhat  cooler  than  their  surround- 
ings. The  heat  thus  absorbed  becomes  latent;  that  is,  it  is 
used  up  in  the  change  of  state  and  does  not  raise  the  tempera- 
ture of  the  liquid.  Other  things  being  equal,  the  greater  the 
surface  exposed,  the  more  rapid  will  be  the  evaporation.  In 
sugar  making,  the  syrup  to  be  evaporated  is  placed  in  large 
shallow  pans  to  facilitate  the  process.  Evaporation  is  also 
promoted  by  removing  the  vapor  as  fast  as  it  is  produced  and 
thus  clearing  the  way  for  other  molecules  of  the  evaporating 
liquid  to  fly  off.  There  is,  as  might  be  expected,  a  consider- 
able difference  in  the,  rate  at  which  different  liquids  evaporate, 
but  all  are  alike  in  requiring  heat  for  the  process.  Liquids 
which  evaporate  rapidly  of  course  take  up  heat  rapidly  and 
feel  colder  than  those  which  evaporate  more  slowly.  If  a 
liquid  disappears  very  quickly  when  exposed  to  the  air,  it  is 
said  to  be  volatile.  Sublimation,  already  mentioned  (§52), 
may  be  considered  as  a  form  of  evaporation  which  takes  place 
in  some  solids  at  a  temperature  lower  than  their  melting  or 

101 


102  SXPEKIMEKTAL.  GENERAL  SCIENCE 

boiling  points.  On  a  eold  day,  ioe  will  sublimate,  and  a  light 
snow  fall  may  thus  disappear  without  making  the  ground  wet. 
Frost  frequently  sublimates  instead  of  melting.  Other  sub- 
stances are  known  which,  owing  to  their  readiness  to  unite 
with  oxygen,  cannot  be  turned  to  gases  under  ordinary  condi- 
tions. When  heated  beyond  a  certain  point  they  do  not  even 
become  liquid  but  form  gaseous  compounds  with  the  oxygen 
in  the  air.  Carbon  and  phosphorus  are  elements  of  this  kind. 
90.  Boiling. — If  the  temperature  of  an  evaporating  liquid 
be  increased  sufficiently,  the  surface  will  not  provide  enough 
space  for  the  escape  of  all  the  vapor  produced.  In  conse- 
quence, bubbles  of  the  vapor  begin  to  form  within  the  body 
of  the  liquid  itself  at  the  point  where  the  heat  is  being  applied. 
When  the  temperature  is  sufficiently  high  to  cause  these  bub- 
bles to  rise  to  the  surface  and  escape  into  the  air,  we  speak  of 
the  process  as  boiling.  For  some  time  before  boiling  begins, 
the  bubbles  of  vapor  may  rise  into  the  cooler  parts  of  the  liquid 
and  there  be  condensed  to  liquid  again.  This  condition  is 
called  simmering.  In  a  liquid  exposed  to  the  air,  boiling  can 
occur  only  when  the  average  speed  of  its  molecules  exceeds 
the  speed  of  the  molecules  of  the  air,  otherwise  they  will  be 
knocked  back  into  the  liquid  again  by  collision  with  the  air 
molecules.  This  explains  why  compressing  the  air  over  a 
boiling  liquid  increases  the  boiling  point.  The  molecules  of 
air  pushed  closer  together  and  moving  at  higher  speeds  make 
the  escape  of  the  molecules  of  the  liquid  more  difficult  (§61). 
If  the  pressure  be  reduced,  however,  the  jnolecules  escape  at 
a  much  lower  temperature.  Water  evaporates  into  a  vacuum 
almost  instantly.  If  the  air  did  not  hinder  evaporation,  we 
would  be  living  in  an  atmosphere  saturated  with  moisture. 
Though  the  pressure  of  a  gas  over  a  liquid  may  retard  the 
evaporation  into  it,  it  does  not  permanently  prevent  it.  As 
much  water  will  eventually  evaporate  into  an  air-filled  space 
as  would  evaporate  into  it  if  the  air  were  not  there. 


EVAPORATION  103 

91.  Gases  and  Vapors. — There  is  no  real  difference  .between 
gas  and  vapor.     As  commonly  regarded,   vapors  will  con- 
dense or  become  liquid  again  at  ordinary  temperatures  while 
gases  will  not.     Thus  steam  would  be  called  a  vapor  but  air 
would  be  called  a  gas.     Water  vapor,  however,  is  as  much  a  gas 
as  is  the  oxygen  or  nitrogen  of  the  air.     Gaseous  water  (steam 
or  water  vapor)  is  invisible.     What  is  commonly  called  steam 
consists  of  fine  particles  of  liquid  water.     By  examining  the 
substance  issuing  from  the  spout  of  a  rapidly  boiling  kettle,  one 
will  note  a  clear  region  between  the  spout  and  the  visible 
matter  coming  from  it.     This  invisible  portion,  only,  is  steam. 
Though  gaseous  water  is  invisible,  many  other  gases  are  not. 
Chlorine  gas  has  a  greenish  hue,  iodine  gas  is  violet,  and  bro- 
mine gas  is  brown. 

92.  Uses  of  Evaporation. — Since  water  in  turning  from  a 
liquid  to  a  gas  takes  up  536  calories  of  heat  for  each  gram  con- 
cerned (§59),  its  evaporation  may  be  made  the  means  of  very 
effective  cooling.     We  sprinkle  the  lawn  or  street  in  summer  to 
cool  the  air,  but  the  mere  presence  of  the  water  does  not  much 
affect  this.     Some  heat,  to  be  sure,  is  absorbed  in  bringing  the 
water  to  the  temperature  of  its  surroundings,  but  it  is  the 
great  amount  of  heat  absorbed  as  it  evaporates  that  produces 
most  of  the  cooling.     On  a  moist  or  "muggy"  day  in  summer, 
we  realize  very  clearly  that  evaporation  is  a  cooling  process. 
On  such  days,  owing  to  the  amount  of  moisture  in  the  air,  the 
perspiration  does  not  readily  evaporate  and  thus  fails  to  cool 
our  bodies.     If  the  air  is  dry,  much  warmer  days  may  be  less 
oppressive,  owing  to  the  rapid  evaporation  of  the  perspiration. 
It  is  this  evaporation  of  the  perspiration  that  regulates  the  tem- 
perature of  the  body,  keeping  it  at  practically  the  same  temper- 
ature throughout  the  year.     In  summer  the  increased  heat 
causes  us  to  perspire  more,  but  even  in  winter  some  moisture  is 
given  off  in  this  way,  as  may  be  easily  seen  by  touching  a  cold 
piece  of  metal  or  sheet  of  glass  with  the  finger  tips  for  a  short 


104  EXPERIMENTAL   GENERAL  SCIENCE 

time.  The  mist  or  the  insensible  perspiration  will  soon  be 
deposited  on  the  object.  The  danger  of  remaining  in  wet 
clothing  is  due  to  the  fact  that  the  evaporation  of  the  moisture 
takes  a  great  amount  of  heat  out  of  the  body  and  so  chills  it. 
If  one  happens  to  be  exercising  vigorously  and  thus  producing 
considerable  amounts  of  heat,  he  is  not  likely  to  become  chilled 
in  wet  clothing.  If  one  happens  to  get  wet,  therefore,  the  best 
way  to  avoid  a  cold  is  to  keep  moving.  In  the  absence  of  ice, 
housewives  often  contrive  to  keep  milk  from  souring  by  cooling 
it  through  evaporation.  The  vessel  containing  the  milk  is 
wrapped  in  a  cloth  which  is  allowed  to  dip  into  a  dish  of  water. 
The  moisture  rises  in  the  cloth  and  evaporates,  taking  the  heat 
out  of  the  milk  for  the  purpose.  A  great  deal  of  the  water 
taken  up  by  plants  is  evaporated  from  the  leaves  and  other 
parts,  thus  keeping  them  cool,  as  our  perspiration  keeps  us 
cool. 

Practical  Exercises 

1.  Put  a  drop  of  water,  a  drop  of  alcohol,  and  a  drop  of  ether  on  the 
back  of  your  hand  and  note  which  evaporates  first.     Which  feels  coldest? 
Why? 

2.  Where  does  a  fog  go  when  it  disappears? 

3.  When  fog  disappears  does  it  warm  or  cool  the  air  (§68)? 


4.  Of  what  advantage  is  it  to  give  people  alcohol  baths  when  they 
have  a  fever? 


5.  How  does  hanging  wet  cloths  in  a  room  cool  it? 

6.  Why  are  wet  soils  likely  to  be  cold  for  a  long  time  in  spring? 

7.  Why  is  it  cooler  on  land  in  a  wet  bathing  suit  than  in  the  water? 


EVAPORATION  105 

8.  All  rivers  run  to  the  sea  and  yet  the  sea  is  never  quite  full.     Why? 

9.  In  tropical  countries,  drinking  water  is  kept  cool  by  being  placed 
in  porous  earthenware  jars  through  the  walls  of  which  part  of  the  water 
escapes  and  evaporates.     How  does  this  keep  the  rest  of  the  water  cool? 

10.  Which  would  register  higher,  a  thermometer  with  its  bulb  covered 
with  a  wet  cloth  or  one  with  its  bulb  dry?     Why? 

11.  How  would  much  moisture  in  the  air  affect  the  height  of  a  wet- 
bulb  thermometer? 

12.  Housekeepers  find  that  water  "boils  away"  faster  on  some  days 
than  on  others.     How  do  you  account  for  this? 

13.  Put  a  crystal  of  iodine  into  a  test-tube  and  heat  gently  over  the 
bunsen  burner.     What  is  the  result  (§52)? 

14.  Account  for  the  fact  that  when  a  piece  of  camphor  gum  is  exposed 
to  the  air,  its  odor  may  soon  be  noticed  at  some  distance  from  the 
substance. 

16.  Explain  how  wet  cloths  hung  out  on  a  cold  day  may  "freeze  dry;" 
that  is,  may  freeze  and  then  dry. 

16.  How  does  fanning  cool  us  when  we  are  warm? 

17.  Why  does  a  baked  potato  weigh  less  than  it  did  when  raw? 

18.  Why  do  clothes  dry  most  rapidly  on  a  windy  day? 

19.  Why  do  strong  winds  rapidly  dry  the  soil? 

20.  When  there  is  no  perceptible  movement  of  the  air,  one  can  often 
discover  which  way  it  is  moving  by  wetting  the  finger  and  holding  it 
up  in  the  air.    Explain. 


CHAPTER  XVI 
MOISTURE  IN  THE  AIR 

93.  Variation  in  Amount. — The  air  always  contains  some 
moisture  but  the  amount  depends  upon  a  variety  of  conditions. 
It  is  greatest,  of  course,  in  the  vicinity  of  large  bodies  of  water 
and  least  in  deserts,  but  in  any  locality  it  may  vary  from  day 
to  day,  being  affected  by  the  prevailing  winds,  the  amount  of 
sunshine,  the  elevation  above  sea  level,  and  the  temperature. 
If  we  place  a  quantity  of  water  in  a  bottle,  and  leave  it  un- 
corked, it  will  soon  escape  into  the  air,  but  if  the  bottle  be 
corked,  the  limit  to  the  evaporation  is  soon  reached  and  the 
rest  of  the  water  remains  in  the  bottom  of  the  bottle.  From 
this  we  discover  that  water  cannot  continue  to  evaporate  into 
a  given  space  for  an  indefinite  period.  As  soon  as  a  space  has 
a  certain  amount  of  water  vapor  in  it,  no  more  can  be  taken 
up  and  we  say  that  it  is  saturated.  If  the  temperature  of  the 
space  is  then  raised,  its  capacity  for  moisture  is  increased  and 
more  will  evaporate  into  it,  but  if  the  temperature  be  lowered, 
its  capacity  is  diminished  and  some  of  the  moisture  must  be 
dropped.  The  temperature  point  at  which  the  water 
vapor  in  a  given  space  begins  to  turn  back  to  liquid  water 
when  the  temperature  is  lowered  is  called  the  dew-point.  The 
dew-point  is  not  a  fixed  point  like  the  freezing  and  boiling 
points,  but  varies  from  day  to  day  or  from  hour  to  hour,  ac- 
cording to  the  amount  of  moisture  in  the  space  and  its  tem- 
perature. When  the  temperature  is  high  and  the  space  nearly 
saturated,  a  very  slight  drop  in  the  temperature  will  cause  some 
of  the  moisture  to  condense  and  return  to  the  liquid  state.  If 
there  is  very  little  moisture  in  the  given  space,  however,  the 

106 


MOISTURE    IN   THE   AIR  107 

temperature  may  drop  many  degrees  without  the  dew-point 
being  reached. 

WEIGHT  IN  GRAINS  OF  WATER  VAPOR  PER  CUBIC  FOOT  AT 
SATURATION 

Temp.  F.  Grains  Temp.  F.  Grains 

0  0.481  55  4.849 

5  0.610  60  5.745      , 

10  0.776  65  6.782 

15  0.986  70  7.980 

20  1.235  75  9.356 

25  1.551  80  10.934 

30  1.935  85  12.736 

35  2.366  90  14.790 

40  2.849  95  17.124 

45  3.414  100  19.812 

50  4.076 

94.  Humidity. — The  amount  of  moisture  actually  present 
in  a  given  quantity  of  air  at  any  time  is  called  its  absolute 
humidity.  The  absolute  humidity  is  usually  expressed  in 
grains  of  water  vapor  per  cubic  foot.  The  ratio  of  the  absolute 
humidity  in  a  given  space  at  a  given  temperature  to  the  amount 
of  moisture  the  space  could  hold  if  saturated  gives  its  relative 
humidity.  When  the  temperature  of  the  air  is  lowered  it  does 
not  affect  the  absolute  humidity  provided  the  dew-point  is  not 
reached,  for  the  mere  lowering  of  the  temperature  cannot 
affect  the  amount  of  moisture  actually  present,  but  since  the 
relative  humidity  is  the  ratio  of  the  amount  present  to  the 
amount  the  space  could  hold  if  saturated,  lowering  the  tempera- 
ture increases  the  relative  humidity  and  raising  the  tempera- 
ture decreases  it.  To  be  called  moist,  the  air  should  have  more 
than  50  per  cent,  of  the  vapor  it  is  capable  of  holding.  The 
amount  of  moisture  in  the  air  over  cultivated  land  areas  is 
between  50  and  60  per  cent.,  and  over  water,  of  course,  it  is 
much  greater.  The  relative  humidity  of  our  dwellings  and 


108 


EXPERIMENTAL   GENERAL   SCIENCE 


school-rooms,  therefore,  should  be  at  least  50  per  cent.  Some 
interesting  phases  of  humidity  are  encountered  when  dwellings 
are  heated  by  furnaces.  When  the  air  is  taken  in  from  out- 
doors, as  it  commonly  is,  the  heat  of  the  fire  causes  it  to  greatly 
increase  in  volume,  but  the  moisture  it  contains  is  not  increased 
in  amount  and  there  is  therefore  much  less  per  cubic  foot  than 
in  the  outside  air.  To  remedy  this,  moisture  is  usually  added 
to  the  air  by  evaporating  water  into  it.  Even  when  such 
means  are  used  the  air  in  our  dwellings  is  seldom  moist  enough. 

Not  only  do  we  feel  warmer  in  moist 
air  above  a  certain  temperature,  but 
the  membranes  of  the  throat  and 
other  respiratory  passages  are  kept 
in  better  condition  and  thus  colds 
and  sore  throats  are  avoided. 

95.  The  Hygrometer. — A  device 
for  measuring  the  moisture  in  the  air 
is  called  a  hygrometer.  One  of  the 
simplest,  called  the  hair  hygrometer, 
is  made  of  a  single  long  hair  from 
which  all  oil  has  been  removed  by 
soaking  it  in  ether.  When  exposed 
to  moist  air  this  absorbs  moisture  and 
contracts,  and  when  it  dries,  it  length- 
ens again.  If  passed  over  a  tiny 
FIG.  35.— Wet-  and  dry-bulb  pulley  and  kept  taut  by  a  small 

weight,  its  shortening  and  lengthen- 
ing may  be  made  to  move  a  hand  on  the  pulley  and  so  indicate 
the  relative  amount  of  moisture  in  the  air.  The  instrument 
most  frequently  used  is  called  a  psychrometer.  It  consists  of 
two  thermometers  that  read  exactly  alike  mounted  together. 
One  thermometer  is  so  arranged  that  its  bulb  may  be  kept 
wet.  As  the  moisture  evaporates,  the  temperature  of  this 
thermometer  is  lowered,  and  if  the  air  is  dry,  the  evaporation 


c 

• 

-120 

3 

720 

-110 

-110 

-100 

100 

-90 

-90 

-80 

-80 

-70 

-70 

-60 

-60 

-50 

'-50 

-40 

-40 

-30 

-30 

-20 

-20 

-10 

10 

-  0 

-   0 

-10 

-  10 

-20 

20 

-30 

-30 

K 

j& 

r 

MOISTURE   IN   THE   AIR  109 

will  of  course  be  rapid  and  the  temperature  registered  will  be 
much  lower  than  if  the  air  were  moist.  The  second  thermom- 
eter registers  the  true  temperature  of  the  air,  and  a  comparison 
of  the  temperatures  registered  by  the  two  thermometers  will 
indicate  the  relative  humidity. 

96.  Forms  of  Condensation. — Rain,  snow,  hail,  fog,  clouds, 
dew,  and  frost  are  some  of  the  different  forms  which  result 
from  a  lowering  of  the  temperature  of  the  air  below  the  dew 
point.  Fog  and  clouds  consist  of  tiny  particles  of  liquid  water 
condensed  from  the  water  vapor  in  the  air.  The  only  differ- 
ence between  them  is  that  one  is  near  the  ground  and  the  other 
at  a  considerable  altitude  above  it.  On  a  mountain  top  a 
cloud  which  drifts  across  it  is  found  to  be  only  a  heavy  fog. 
Clouds  or  fogs  always  occur  when  the  temperature  of  the  air 
falls  below  its  saturation  point.  A  certain  amount  of  dust  in 
the  air  seems  necessary  for  the  formation  of  clouds,  each  parti- 
cle of  dust  forming  a  nucleus  upon  which  moisture  can  con- 
dense. When  single  clouds  are  formed  in  the  sky,  each  is  at 
the  top  of  a  column  of  moist  air  which  has  risen  high  enough 
to  be  condensed.  Other  clouds  may  be  formed  by  moist  winds 
blowing  into  colder  regions  and  their  moisture  being  condensed. 
Rain  occurs  when  the  particles  in  the  cloud  become  so  large 
from  further  condensation  that  they  no  longer  float  in  the  air. 
If  the  raindrops  fall  into  layers  of  warmer  air,  they  may  be 
again  evaporated  without  reaching  the  earth.  Over  very  hot 
regions,  such  rain  storms  far  above  the  earth  are  occasionally 
observed.  Dew  is  the  moisture  in  the  air  condensed  on  objects 
on  or  near  the  ground.  It  is  incorrect  to  assume,  however,  that 
all  the  moisture  found  on  grass  and  other  herbage  in  the  early 
morning  is  dew.  A  great  deal  of  it  is  moisture  given  off  by 
the  plants  themselves  in  the  form  of  liquid  water.  Rain  and 
dew  occur  only  when  the  dew-point  is  above  the  freezing  point. 
When  the  dew-point  is  lower  than  the  freezing  point,  hail, 
snow,  or  frost  results  when  condensation  occurs.  It  may  be 


110  EXPERIMENTAL  GENERAL  SCIENCE 

noted  that  this  latter  phase  of  condensation  is  a  form  of 
sublimation. 

97.  Cloud  Forms. — A  considerable  number  of  cloud  forms 
have  been  distinguished  and  named,  the  principal  ones  being 
easily  recognized.  Highest  of  all  are  certain  thin  wisps  of 
cloud  commonly  called  "mares'  tails"  and  known  to  the 
meteorologists  as  cirrus  clouds.  They  may  be  nearly  ten  miles 
above  the  earth  and  are  supposed  to  consist  of  small  ice 
crystals.  The  cirro-cumulus  clouds  produce  the  familiar 
"mackerel  sky."  They  are  in  the  form  of  short,  often  curved, 
sections  and  are  nearly  as  high  in  the  air  as  the  cirrus  clouds. 
Cumulus  clouds  are  the  fleecy  day  clouds  which  appear  like 
great  piles  of  wool  in  the  sky.  They  are  much  nearer  the 
earth — seldom  more  than  a  mile  high.  Cumulus  clouds  may 
continue  to  enlarge  until  they  form  the  cumulo-nimbus  clouds 
called  "thunder  heads"  which  produce  most  of  our  thunder 
storms.  The  nimbus  cloud-,  found  at  an  altitude  of  less  than 
a  mile,  is  the  ordinary  rain  cloud  which  produces  the  all-day 
rains.  Lowest  of  all  are  the  stratus  clouds — flat,  level  clouds 
of  no  distinct  form,  seen  most  frequently  in  the  early  part  of 
the  day.  They  are  seldom  more  than  half  a  mile  high,  and 
usually  disappear  as  the  day  advances.  Fog  may  be  called 
a  stratus  cloud  near  the  ground. 

Practical  Exercises 

1.  Into  a  metal  cup  or  can  with  a  brightly  polished  outer  surface  put 
a  quantity  of  cold  water.     Then  drop  pieces  of  ice  into  the  water  stirring 
it  with  a  thermometer  until  a  film  of  moisture  begins  to  appear  on  the 
outside  of  the  vessel.     The  reading  of  the  thermometer  at  this  instant 
will  give  the  approximate  temperature  of  the  dew-point  in  the  place 
where  the  experiment  is  made.     What  was  the  temperature  of  the 
dew-point  in  your  experiment? 

2.  Account  for  the  formation  of  frost  on  window  panes  in  cold  weather 
(§93). 


MOISTURE    IN   THE    AIR  111 

3.  Why  does  no  frost  form  on  the  outside  of  window  panes  in  cold 
weather? 


4.  How  can  you  tell,  by  consulting  the  wet-  and  dry-bulb  ther- 
mometers, whether  the  dew-point  at  the  time  is  high  or  low? 

6.  Examine  the  wet-  and  dry-bulb  thermometers  in  your  school  and 
see  if  the  relative  humidity  is  sufficiently  high.  If  the  school  has  no 
wet-bulb  thermometer  one  can  easily  be  made  from  an  ordinary 
thermometer. 

6.  Why  is  it  incorrect  to  say  that  dew  falls? 

7.  If  the  dew-point  is  above  40°F.  on  autumn  evenings  no  frost  is 
expected.     How  does  the  formation  of  dew  prevent  frost? 


8.  When  you  notice  single  clouds  near  the  horizon  on  a  warm  day 
you  find  that  the  under  side  is  nearly  level.  How  do  you  account  for 
this? 


9.  Explain  how  high  mountains  prevent  moisture-bearing  winds  from 
carrying  moisture  beyond  them  (§§63,  93). 

10.  From  a  geography,  select  and  name  a  desert  that  is  due  to  the 
cause  mentioned  in  question  9. 

11.  Clouds,  being  composed  of  particles  of  liquid  water,  are  heavier 
than  air.     Why  then  do  they  not  descend  to  the  earth? 

12.  If  a  wind  moves  from  a  cold  region  into  a  warmer  one,  will  its 
capacity  for  moisture  be  increased  or  diminished? 

13.  Will  it  be  likely  to  bring  clear  or  cloudy  weather?    Why? 

14.  What  wind  ought  to  bring  clouds  in  your  region? 


112  EXPERIMENTAL   GENERAL   SCIENCE 

15.  What  wind  blows  before  a  storm  in  your  region? 

16.  Why  are  summer  thunder  storms  most  likely  to  occur  after  the 
sun  has  begun  to  go  down? 

17.  Why  is  it  foggy  in  the  North  Atlantic  in  the  vicinity  of  icebergs? 

18.  Explain  the  "banner  cloud"  that  often  streams  away  from  a 
mountain  top  opposite  the  side  from  which  the  wind  is  blowing. 


FIG.  36. — Banner-cloud  diagram. 

19.  Why  does  little  rain  fall  in  the  Sahara  Desert  when  moist  winds 
from  the  Mediterranean  Sea  often  blow  over  it? 


20.  Why  can  you  "see  your  breath"  on  a  cold  day? 


21.  Why  is  fog  more  frequent  in  river  valleys  and  along  large  bodies 
of  water  than  elsewhere? 


22.  Explain  the  formation  of  the  cloud  which  sometimes  appears  over 
burning  building. 

23.  Why  is  fog  more  likely  to  form  near  cities  than  in  the  country? 


CHAPTER  XVII 


CAPILLARITY  AND  OSMOSIS 

98.  Water  Surfaces. — A  liquid  is  said  to  have  its  free  surface 
level,  but  this  does  not  mean  that  it  would  conform  to  a 
straight  line.  Since  the  earth  is  a  sphere,  the  water  level  must 
constantly  curve.  This  curvature  may  easily  be  seen  on  a 
long  straight  stretch  of  water  such  as  a  lake  or  canal.  If  a 
telescope  or  field  glass  is  fixed  exactly  horizontal  at  a  certain 
distance  above  the  water  and  a  target  a  mile  or  so  away  is 
placed  at  the  same  height  above 
the  water,  it  cannot  be  seen 
through  the  glass,  owing  to  the 
curvature.  A  water  surface  is 
considered  level,  however,  when  it 
conforms  to  the  curvature  of  the 
earth.  A  well-known  proverb 
runs  to  the  effect  that  "water 
seeks  its  level."  We  find  this  _ _ 

true  no  matter  what  the  shape  of       FIG.  37.— Capillary  attraction 

the  vessel  containing  it  happens  fe -*?***  (Tower,  Smith  and 
to  be.  If  vessels  of  various  shapes 

and  sizes  are  connected  at  the  bottom  in  such  a  way  that 
liquid  is  free  to  move  from  one  to  the  other,  pouring  water 
into  any  of  the  vessels  will  cause  it  to  rise  to  the  same  height 
in  all  of  them.  There  are  certain  conditions,  however,  in 
which  water  is  not  exactly  level,  even  in  ordinary  vessels.  If 
we  stand  a  sheet  of  glass  on  edge  in  a  dish  of  water  for  instance, 
and  examine  the  point  at  which  the  surface  of  the  water  comes 
into  contact  with  it,  we  find  that  it  curves  upward  here.  The 

8  113 


114  EXPERIMENTAL    GENERAL   SCIENCE 

same  thing  occurs  when  a  glass  is  partly  filled  with  water.  The 
surface  slopes  upward  wherever  it  is  in  contact  with  the  glass. 
If  mercury  instead  of  water  is  used,  the  surface  curves  down- 
ward instead  of  upward.  Experiments  with  various  liquids 
have  shown  that  whenever  a  liquid  wets  or  clings  to  the  walls 
of  the  vessel  in  which  it  is  contained,  the  curvature  is  upward, 
and  when  it  does  not  wet  the  surface,  the  curvature  is  down- 
ward. The  phenomenon  is  best  shown  by  means  of  small  glass 
tubes  of  different  sizes.  When  several  of  these  are  stood  in 
the  same  dish  of  water,  the  liquid  always  rises  highest  in  the 
smallest  tubes.  In  mercury,  the  surface  is  depressed,  the 
greatest  depression  occurring  in  the  smallest  tubes.  The  water 
rises  in  the  tubes  because  of  a  certain  attraction  between  it  and 
the  tubes,  which  is  known  as  capillarity.  Heat,  which  lessens 
the  attraction  of  molecules  for  one  another,  has  a  tendency  to 
reduce  the  effects  of  capillarity.  The  phenomena  were  first 
studied  in  tubes  with  very  fine  hair-like  openings,  hence  the 
name  from  the  Latin  word  capillus,  meaning  a  hair. 

99.  Absorption  by  Capillarity. — A  great  deal  of  what  we  call 
absorption  is  explained  by  capillarity.     Wood  takes  up  glue 
or  varnish,  sponges  soak  up  water,  blotters  take  up  ink — in 
fact,  any  substance  with  small  openings  in  it  will  absorb 
liquids  when  in  contact  with  them.     If  one  end  of  a  towel  is 
left  in  a  dish  of  water,  the  water  will  creep  up  in  the  capillary 
spaces  in  the  towel  and  soon  leave  the  dish  empty.     Most 
of  the  moisture  used  by  plants  moves  through  the  soil  by  cap- 
illarity.    It   is   by  this   means   that  plants  obtain  moisture 
at  some  distance  from  their  roots.     When  the  moisture  in  the 
soil  close  to  the  roots  has  been  taken  up,  more  moves  in  by 
capillarity. 

100.  Deliquescence. — Some    crystalline    substances    have 
such  an  affinity  for  moisture  that  they  rapidly  absorb  it  from 
the  air  and  are  thus  dissolved.     A  piece  of  sodium  hydroxide 
liquefies  in  a  few  minutes  if  exposed  to  the  air  and  must  be 


CAPILLARITY   AND    OSMOSIS  115 

kept  in  moisture-proof  receptacles.  Sulphuric  acid  rapidly 
gains  in  weight  by  absorbing  moisture  from  the  air,  and  quick- 
lime slacks  in  the  same  way.  When  a  substance  thus  dissolves 
it  is  said  to  deliquesce  or  to  be  deliquescent.  If  it  only  takes  on 
additional  moisture,  it  is  said  to  be  hygroscopic.  Most  mosses 
and  lichens  are  hygroscopic.  The  lichens,  especially,  get 
much  of  the  moisture  used  in  their  life  processes  from  the 
moisture  in  the  air.  There  are  also  certain  crystalline  sub- 
stances which  act  in  a  manner  exactly  opposed  to  deliques- 
cence when  exposed  to  the  air.  Instead  of  taking  on  more 
moisture  they  give  up  what  they  have  and  fall  into  a  fine  pow- 
der. Such  substances  are  said  to  be  efflorescent. 

101.  Shrinking  and  Warping. — Many  vegetable  and  animal 
fibers  have  the  property  of  becoming  shorter  and  thicker  when 
wet.     This  is  taken  advantage  of  in  shrinking  cloth  to  make 
the  threads  thicker  and  closer  together.     The  same  thing 
happens  when  boards  warp.     If  one  side  becomes  moist  the 
swelling  fibers  cause  that  side  to  become  larger  and  curve 
toward  the  dry  side.     One  of  the  chief  reasons  for  painting  and 
varnishing  woodwork  is  to  prevent  the  absorption  of  water  and 
the  consequent  warping. 

102.  Osmosis. — There  is  still  another  way  in  which  water 
moves  in  substances  against  the  force  of  gravity.     If  two 
liquids  of  different  density,  that  ordinarily  mix,  be  separated 
by  a  membrane  such  as  parchment  paper,  hog's  bladder,  or  the 
cell  walls  of  animals  or  plants,  they  usually  begin  to  flow 
through  the  separating  membrane  and  continue  to  do  so  until 
the  liquids  on  each  side  of  it  have  the  same  density.     This  is 
known  as  osmosis.     The  liquid  of  less  density  will,  of  course, 
go  through  the  membrane  more  rapidly  than  the  denser  liquid 
and  for  a  time  may  increase  the  bulk  of  the  latter  very  con- 
siderably, but  as  the  density  of  the  two  liquids  becomes  more 
nearly  uniform,  the  level  of  the  liquids  becomes  the  same.     An 
interesting  illustration  of  osmosis  may  be  had  by  filling  a  this- 


116 


EXPERIMENTAL   GENERAL   SCIENCE 


tie-tube  half  full  of  molasses,  tying  a  piece  of  parchment  paper 
or  other  membrane  over  the  open  end,  and  inverting  it  in  a 
jar  of  clear  water.  The  water  at  once  begins  to  flow  into  the 
thistle-tube  through  the  membrane,  and  often  increases  the 
bulk  of  the  molasses  so  much  that  it  will  rise  in  the  stem  of  the 
thistle-tube  18  or  20  feet  against  gravity.  As  the  molasses 
slowly  diffuses  out  into  the  water,  the  density  of  the  two  liquids 
gradually  becomes  the  same  and  the 
column  of  liquid  falls.  Gases  separated 
by  a  membrane  behave  in  the  same 
way,  but  the  phenomena  are  most 
noticeable  in  liquids.  To  certain  kinds 
of  liquids  and  gases,  membranes  may 
be  semi-permeable;  that  is,  they  may 
allow  fluids  to  pass  but  retain  sub- 
stances dissolved  in  them.  The  cell 
walls  of  plants  with  their  lining  of  pro- 
toplasm act  in  this  way,  and  while  per- 
mitting the  inflow  of  water  and  food 
^  materials,  refuse  to  allow  the  matter 
FIG.  38.— Method  of  within  the  cells  to  escape. 

setting  up  osmosis  experi- 

ment-  Practical  Exercises 

1.  Fasten  two  strips  of  glass  together  in  narrow  V-shape  using  a 
small  piece  of  wood  to  keep  the  V  open.  Stand  the  strips  on  edge  in 
a  dish  of  water  and  explain  the  behavior  of  the  liquid. 


2.  Account  for  the  fact  that  if  you  touch  one  corner  of  a  lump  of 
sugar  to  a  liquid,  such  as  coffee,  the  liquid  will  spread  through  the 
entire  lump. 


3.  What  use  is  made  of  capillarity  in  the  wicks  of  oil  lamps? 

4.  Why  is  writing  paper  "sized"  while  blotting  paper  is  not? 


CAPILLARITY  AND   OSMOSIS  117 

6.  How  does  the  split  in  the  pen  make  the  ink  flow  more  uniformly? 


6.  From  which  would  you  expect  more  water  to  evaporate,  a  compact 
or  a  loose  soil,  both  being  equally  wet?     Why? 


7.  In  which  would  you  expect  the  soil  water  to  rise  higher,  a  sandy 
or  a  clay  soil?     Why? 


8.  How  would  a  mulch  of  straw,  leaves,  or  even  dry  earth,  prevent 
the  moisture  in  the  soil  from  escaping? 


9.  In  planting  small  seeds,  it  is  customary  to  firm  the  soil  over  them 
to  keep  them  moist.     How  does  firming  the  soil  accomplish  this? 

10.  Why  is  salt  likely  to  become  lumpy  in  wet  weather? 


11.  When  moss  is  soft  to  the  tread,  it  is  regarded  as  a  sign  of  an 
approaching  storm.     Why? 


12.  When  clothes  are  sprinkled  for  ironing,  why  are  they  usually 
rolled  up  and  allowed  to  lie  for  a  short  time? 


13.  Why  do  doors,  drawers,  and  windows  often  stick  in  wet  weather? 


14.  In  old  houses,  the  floors  and  stairways  often  snap  and  creak  before 
a  change  in  the  weather.     Explain. 


15.  In  quarries,  pieces  of  rock  are  sometimes  broken  off  by  the  simple 
expedient  of  drilling  several  holes  in  a  row  where  the  break  is  desired, 
fitting  each  hole  with  a  plug  of  dry  wood  and  then  wetting  the  plugs. 
Explain. 

16.  Why  may  a  wooden  tub  or  barrel  fall  to  pieces  if  not  kept  moist  ? 


118  EXPERIMENTAL   GENERAL   SCIENCE 

17.  When  raisins  or  other  dried  fruits  are  thrown  into  water  they 
increase  in  size.     Explain. 

18.  If  sugar  be  sprinkled  over  berries  or  other  juicy  fruits,  a  quantity 
of  juice  soon  appears  in  the  dish.     Account  for  this. 

19.  When  fresh  fruits  are  put  into  thick  syrup  in  preserving,  the  fruit 
soon  shrivels.     Why? 

20.  How  does  putting  salt  on  grass  kill  it? 

21.  The  crispness  of  celery,  lettuce  and  other  vegetables  is  increased 
by  putting  them  hi  fresh  water.     Explain. 


22.  In  making  extracts  the  druggist  cuts  the  substance  he  is  working 
with  into  small  bits,  covers  them  with  alcohol  or  water  and  lets  them  stand 
for  a  time.  How  does  this  extract  the  matter  desired? 


I.  Should  meat  intended  for  a  stew  be  rapidly  or  slowly  cooked? 


24.  Will  salting  the  water  in  which  a  piece  of  meat  is  stewing,  help 
or  hinder  the  extraction  of  its  flavor? 


25.  Account  for  the  flow  of  sap  from  trees  when  injured  in  spring. 


CHAPTER  XVIII 
PRESSURE  OF  THE  AIR 

103.  The  Atmosphere. — The  gaseous  matter  which  envelops 
the  earth  and  penetrates  some  distance  below  the  surface  is 
called  the  atmosphere.    We  commonly  speak  of  it  as  the  air. 
Air  consists  almost  entirely  of  two  gases,  oxygen  and  nitrogen, 
which  occur  as  a  mechanical  mixture  and  not  as  a  chemical 
compound.     Of  this  mixture,  oxygen  forms  about  21  per  cent, 
and  nitrogen  about  77  per  cent.     There  are  also  present  in  the 
air,  carbon  dioxide,  water  vapor,  traces  of  argon  and  other 
rare  gases,  ammonia,  dust,  and  the  spores  of  plants.     In 
addition  to  the  oxygen  and  nitrogen,  the  only  constituents 
worth  notice  at  this  time  are  carbon  dioxide  and  water  vapor. 
Carbon  dioxide,  though  a  product  of  all  ordinary  burning, 
forms  only  about  iKoo  °f  1  Per  cent.;  that  is,  only  three  parts 
in  10,000  of  dry  air.     Water  vapor  varies  in  amount  as  we 
have  already  seen,  and  is  usually  present  in  much  larger 
quantities,  often  as  much  as  3  per  cent.     Since  the  amount  of 
water  vapor  present  depends  upon  the  time  and  locality,  it 
need  not  be  considered  at  this  point.     In  ten  thousand  parts 
of  average  air,  therefore,  the  chief  components  are  represented 
about  as  follows: 

Nitrogen. 7,700  parts 

Oxygen 2,100  parts 

Argon 100  parts 

Carbon  dioxide 3  parts 

104.  Weight  of  the  Air. — Though  extremely  light  in  com- 
parison with  other  familiar  substances,  air,  being  a  form  of 

119 


120  EXPERIMENTAL   GENERAL   SCIENCE 

matter,  has  weight.  At  sea  level,  a  cubic  foot  of  air  weighs 
about  an  ounce  and  a  quarter.  The  total  weight  of  the  atmos- 
phere is  some  5,000,000,000,000,000  tons.  A  column  of  air  an 
inch  square,  extending  from  sea  level  upward  as  far  as  the  air 
goes,  weighs  nearly  15  pounds;  that  is,  it  presses  downward 
or,  rather,  is  pulled  downward  by  gravity,  with  a  force  of 
nearly  15  pounds  to  the  square  inch.  Since  air,  like  other 
gases,  is  easily  compressed,  the  air  at  sea  level  is  densest, 
owing  to  the  pressure  of  other  air  above  it,  but  this  density 
and  pressure  grows  steadily  less  as  we  go  upward.  The  pres- 
sure of  the  air  at  sea  level  is  often  taken  as  a  standard  for 
measuring  other  pressures,  and  is  spoken  of  as  the  pressure 
of  one  atmosphere. 

105.  Function  of  the  Air  Constituents. — Oxygen  is  the  life- 
giving  principle  of  the  air,  for  without  it  neither  animals  nor 
plants  could  exist.  Its  union  with  carbon  in  our  bodies  keeps 
us  warm,  and  similar  unions  elsewhere  supply  most  of  the 
energy  used  in  the  world.  Though  oxygen  is  of  such  great 
importance,  it  would  be  harmful  if  it  occurred  in  greater 
amounts,  since  combustion  or  oxidation  would  go  on  altogether 
too  fast.  A  cook-stove  would  burn  up  in  pure  oxygen.  The 
most  important  use  of  nitrogen,  so  far  as  man  is  concerned,  is 
to  dilute  the  oxygen  and  thus  put  a  damper  on  its  activities. 
It  is  the  nitrogen  which  gives  the  air  most  of  its  weight  and 
pressure,  and  makes  it  possible  for  it  to  turn  windmills,  move 
sailboats,  and  the  like.  In  tornadoes,  the  air  may  move  at 
such  a  high  speed  as  to  uproot  trees,  destroy  buildings,  and 
do  many  curious  things,  such  as  driving  straws  through  boards. 
The  pressure  of  rapidly  moving  air  also  makes  heavier-than- 
air  flying  machines  possible.  So  long  as  they  are  passing 
rapidly  through  the  air,  the  pressure  is  sufficient  to  keep  them 
up.  Carbon  dioxide,  in  addition  to  being  the  material  from 
which  the  bulk  of  the  solid  parts  of  plants  is  made,  also  absorbs 
much  of  the  heat  radiated  from  the  earth,  and  together  with 


PRESSUKE    OF  THE   AIR 


121 


water  vapor  and  dust,  acts  as  a  blanket  to  keep 
in  the  heat  and  prevent  sudden  changes  in  the 
temperature  of  the  air. 

106.  The  Barometer. — Owing  to  various 
causes,  the  pressure  of  the  air  in  a  given  locality 
varies  from  day  to  day.  The  most  important  of 
these  causes  are  differences  in  the  temperature 
of  the  air  and  varying  amounts  of  water  vapor  in 
it.  Moist  air  is  lighter  than  dry  air,  and  warm 
air  lighter  than  cold.  Variations  in  air  pressure 
are  measured  by  the  barometer.  This  instrument 
consists  of  a  glass  tube  closed  at  the  upper  end, 
and  filled  with  mercury.  The  lower  end  of  the 
tube  dips  into  a  dish  of  mercury  and  the  pressure 
of  the  air  on  the  surface  of  the  dish  causes  the 
mercury  in  the  barometer  tube  to  rise  and  fall 
with  each  variation  in  pressure.  A  scale  is 
attached  to  the  upper  end  of  the  tube  by  means 
of  which  the  variations  may  be  ascertained. 
A  sliding  indicator  and  scale  called  a  vernier  is 
attached  to  the  tube  for  exact  measurements. 
At  sea  level  the  pressure  of  the  air  is  sufficient 
to  support  a  column  of  mercury  760  millimeters 
or  30  inches  long.  With  each  rise  of  90  feet 
above  sea  level  the  mercury  lowers  about  Ho 
inch.  The  daily  fluctuations  of  the  barometer 
seldom  vary  more  than  a  few  tenths  of  an  inch. 
This,  however,  represents  a  considerable  differ- 
ence in  pressure.  A  difference  of  one  inch  in 
barometer  readings  indicates  a  difference  of 
more  than  a  million  tons  over  a  square  mile.  FIG.  39.— 
Although  mercury  is  the  most  satisfactory  fluid  barometer^ 
for  use  in  barometers,  any  other  liquid  might  (Tower,  Smith 

.     ,.  ,    .  ,.   ,,          and  Turton.') 

serve  to  indicate  pressure,  but  in  case  a  lighter 


122  EXPERIMENTAL   GENERAL   SCIENCE 

liquid,  such  as  water  or  alcohol  were  used,  the  tube  would  have 
to  be  very  much  longer  in  order  to  accommodate  an  equal 


FIG.  40. — An  aneroid  barometer.     (Tower,  Smith  and  Turton.) 


FIG.  41. — The  barograph. 

weight  of  the  liquid.  The  aneroid  barometer  is  a  more  portable 
instrument  for  measuring  pressure.  It  consists  of  a  thin- wall ed , 
air-tight  flat  metal  box,  with  a  thin  corrugated  top,  from  which 


PRESSURE    OF   THE   AIR 


123 


some  of  the  air  has  been  removed.  As  the  atmospheric  pres- 
sure varies,  the  top  of  the  box  rises  or  falls,  and  this  motion  is 
communicated  by  a  spring  and  levers  to  a  hand  moving  over 
a  scale,  which  indicates  the  pressure.  Since  this  style  of 
barometer  is  easily  carried  about,  it  is  frequently  used  in 
estimating  the  height  of  mountains,  etc.  The  barograph  is 
essentially  an  aneroid  barometer  with  an  indicator  adapted 
to  making  a  continuous  record  on  a  moving  strip  of  paper. 


FIG.  42. — Lift  pump.     (Duff.)         FIG.  43. — Force  pump.     (Duff.) 

107.  Lift  Pumps  and  Siphons. — The  ordinary  lift  pump  for 
raising  water  and  other  liquids  above  their  natural  level, 
makes  use  of  the  pressure  of  the  air.  The  pump  has  a  plunger 
and  valves  by  means  of  which  the  air  is  removed  from  the 
pipe  extending  down  into  the  liquid,  and  the  pressure  of  the 
air  then  forces  the  liquid  to  rise  in  the  pipe.  Liquids  will  not 
rise  to  any  height,  however,  for  the  air  only  presses  upward  with 
a  force  of  about  15  pounds  to  the  square  inch.  At  sea  level, 


124 


EXPERIMENTAL   GENERAL   SCIENCE 


this  is  only  sufficient  to  force  water  up  to  a  height  of  about 
34  feet.  The  pumps  which  raise  water  to  much  greater  heights 
are  called  force  pumps.  In  such  pumps,  the  upward  stroke  of 
the  piston  causes  more  water  to  rise  in  the  pipe,  and  the  down- 
ward stroke  closes  the  valve  and  forces  the  water  to  flow 
through  another  pipe  to  higher  levels.  Even  in  this  type  of 
pump,  the  valves  and  plunger  must  be  located  near  enough 
to  the  surface  of  the  liquid  to  take  advantage  of  the  air 
pressure.  A  siphon  is  a  device 
for  lifting  liquids  against  gravity 
with  the  aid  of  air  pressure. 
It  is  simply  a  bent  tube  with 
one  end  in  the  liquid  to  be 
siphoned  and  the  other  extend- 


FIG.  44.— Siphon.     (Duff.) 


FIG.  45. — Water  does  not  run  out 
when  tumbler  is  inverted.  (Touvr, 
Smith  and  Turton.) 


ing  outside  to  a  lower  level.  When  the  air  is  removed  from  the 
tube,  either  by  pumping  it  out  or  by  filling  the  tube  with  the 
liquid,  the  liquid  in  the  vessel  will  run  out,  though  it  may  have 
to  rise  a  considerable  distance  to  do  it.  The  air  pressure  on 
each  end  of  the  tube  is,  of  course,  practically  the  same,  but 
since  the  outer  end  of  the  siphon  is  always  longer  and  lower, 
it  contains  a  greater  weight  of  water  which,  beginning  to  run 
out,  tends  to  form  a  vacuum  at  the  bend,  but  this  is  immedi- 
ately filled  by  more  water  which  is  pushed  up  by  the  air 
pressure  over  the  liquid  in  the  vessel,  and  so  the  siphon  con- 


PRESSURE   OF  THE   AIR  125 

tinues  to  run.  Siphons  are  used  in  emptying  tubs,  barrels, 
cisterns,  and  in  removing  liquid  from  bottles,  and  the  like, 
without  disturbing  the  sediment  in  the  bottom,  and  for  many 
other  purposes. 

Practical  Exercises 

1.  Press  a  drinking  glass  or  test-tube,  mouth  down,  into  a  vessel  of 
water.     Why  does  the  water  not  fill  it? 

2.  Why  is  a  so-called  empty  bottle  not  really  empty? 

3.  Stop  up  one  end  of  a  glass  tube  with  the  finger,  fill  it  with  water 
and  invert  it,  placing  the  open  end  in  a  dish  of  water.     Why  does  the 
water  not  run  out? 


4.  Remove  your  finger  from  the  end  of  the  tube.    Why  does  the  water 
now  run  out? 

5.  Fill  a  drinking  glass  with  water,  cover  with  a  card  or  piece  of  stiff 
paper  and,  holding  the  paper  with  one  hand,  invert  the  glass.     Why  does 
the  water  not  run  out  when  the  hand  is  removed? 

6.  If  the  glass  in  the  above  experiment  were  exactly  an  inch  square 
in  cross-section,  how  many  pounds  of  water  could  be  supported  in  this 
way? 


7.  Suppose  the  experiment  in  exercise  5  had  been  performed  with 
mercury  instead  of  water.  Would  the  pressure  have  held  up  as  great  a 
volume  of  mercury?  Why? 


8.  Examine  the  nearest  barometer  and  find  out  how  high  a  column 
of  mercury  the  air  is  able  to  support  at  the  time  the  observation  is 
made. 


9.  If  it  is  less  than  760  millimeters,  account  for  the  difference  noted 
(§104). 


126  EXPERIMENTAL   GENERAL   SCIENCE 

10.  If  the  barometer  had  been  made  with  water  instead  of  mercury, 
would  the  column  of  liquid  have  been  longer  or  shorter?     Why? 

11.  Would  the  variations  in  the  height  of  the  column  of  water  be 
greater  or  less  than  in  the  mercury  column?     Why? 


12.  If  a  bottle  is  corked  at  sea  level  and  opened  on  a  mountain  top 
will  more  air  enter  or  some  come  out?     Why? 


13.  Fill  a  bottle  with  water  and  cork  with  a  two-hole  stopper.  Place 
a  finger  over  one  hole  in  the  stopper  and  invert  the  bottle.  Why  does 
the  water  not  run  out? 


14.  Why  does  the  water  run  out  when  the  finger  is  removed? 


15.  In  drinking  liquid  through  a  straw,  one  removes  the  air  from  the 
straw  and  the  liquid  rises  into  the  mouth.     Explain. 


16.  In  drawing  liquids  from  a  barrel  or  in  pouring  them  from  a  closed 
can,  the  liquid  will  not  run  smoothly  unless  the  cap  on  the  can  or  the 
bung  in  the  barrel  is  loosened.  Why? 


17.  Why  do  liquids  run  so  irregularly  from  a  bottle  or  jug? 


18.  Over  how  high  a  structure  ought  one  to  be  able  to  siphon  water 
at  sea  level? 


19.  Could  one  siphon  alcohol  or  kerosene  over  a  higher  structure  than 
he  could  siphon  water?     Why? 


20.  When  a  break  is  made  in  the  skin,  blood  runs  out.  Does  this 
indicate  a  pressure  within  the  body  greater  or  less  than  15  pounds  to 
the  square  inch? 


PRESSURE    OF   THE    AIR  127 

21.  What  effect  would  moisture  in  the  air  be  likely  to  have  on  the 
height  of  the  mercury  in  the  barometer? 

22.  Which  do  you  infer  that  a  falling  barometer  indicates,  fair  or 
stormy  weather? 

23.  Why  does  smoke  fail  to  rise  well  from  chimneys  just  before  a 
storm? 


24.  Why  may  the  stove  fail  to  have  a  good  draft  on  a  rainy  day? 


25.  Spread  out  one  hand,  palm  downward,  and  hold  a  piece  of  paper 
about  two  inches  square  up  against  the  first  and  middle  fingers  where 
they  join  the  hand.  Blow  downward  between  the  fingers  and  the 
paper  will  remain  in  position  without  being  held,  as  long  as  one  blows. 
The  breath  makes  a  partial  vacuum  on  the  upper  side  of  the  paper. 
Explain  the  pressure  that  holds  the  paper  in  place  when  it  is  being  blown 
upon. 


26.  In  the  vacuum  cleaner,  a  rapidly  revolving  fan,  consisting  of  a 
wheel  with  curved  blades,  makes  a  partial  vacuum  in  the  interior  of  the 
machine.  Explain  >*  >w  this  causes  the  dirt  to  be  swept  into  the  cleaner. 


27.  The  system  of  pipes  that  carry  away  the  dust  from  wood-working 
machinery,  emery  wheels,  and  the  like,  is  essentially  part  of  a  huge 
vacuum  cleaner.  A  similar  system  of  pipes  is  often  used  in  ventilating 
mines  and  large  buildings,  the  impure  air  being  pumped  out  by  this 
means.  Explain  how  this  causes  the  fresh  air  to  enter. 


28.  The  electric  fan  works  on  the  principle  of  the  vacuum  cleaner, 
though  in  this  case,  it  is  the  outflowing  currents  of  air,  instead  of  those 
flowing  in,  that  we  value.     Where  is  the  partial  vacuum  that  is  produced 
by  the  fan  located? 

29.  Where  is  the  partial  vacuum  in  an  atomizer? 


128  EXPEEIMENTAL  GENERAL  SCIENCE 

30.  Why  may  a  wind  blowing  across  a  chimney  cause  a  strong  upward 
draft  in  it? 


31.  At  the  mouth  of  large  caves,  a  current  of  air  flows  outward  or 
inward  at  an  approaching  change  of  the  weather.     In  which  direction 
do  you  infer  the  current  of  air  will  flow  just  before  stormy  weather? 
Why? 

32.  In  correcting  barometer  readings,  it  is  customary  to  add  certain 
amounts  to  the  readings  of  all  places  above  sea  level.     Why  is  this 
necessary  in  comparing  the  pressure  at  different  places? 

33.  Why  is  it  necessary  to  correct  the  barometer  readings  for  tem- 
perature? 

34.  What  is  the  total  air  pressure  on  the  nearest  book?    Why  can 
you  lift  the  book  from  the  table? 

36.  How  does  the  varying  air  pressure  ventilate  the  soil? 


CHAPTER  XIX 
SOLUTIONS 

108.  Solutes  and  Solvents. — When  a  quantity  of  a  solid, 
such  as  salt,  is  shaken  up  in  water,  it  soon  disappears  in  the 
liquid,  or  as  we  say,  it  dissolves  or  goes  into  solution.  If  we  test 
the  solution  thus  made,  we  find  that  the  solid  is  evenly  dis- 
tributed through  it,  for  all  parts  are  equally  salty.  Other 
soluble  substances  may  now  be  added  to  this  solution  and  in 
every  instance  they  act  as  the  salt  did  and  become  evenly 
distributed  through  it.  The  substance  that  disappears  in 
another  in  this  way  is  called  the  solute,  and  the  substance  in 
which  it  disappears  is  the  solvent.  It  must  not  be  assumed, 
however,  that  because  one  liquid  will  dissolve  a  given  solid, 
that  it  will  dissolve  all  others.  As  a  matter  of  fact,  there  are 
many  exceptions  to  this  rule.  Water,  for  instance,  will  dis- 
solve salt,  but  it  will  not  dissolve  camphor.  Alcohol,  on  the 
other  hand,  will  dissolve  camphor  but  not  salt.  Water  is  the 
best  solvent  known;  that  is,  it  will  dissolve  the  greatest  num- 
ber of  substances,  but  alcohol,  ether,  and  some  acids  are  not 
far  behind  it  in  this  respect.  Water  will  not  dissolve  fats, 
waxes,  gums,  or  resins,  though  these  readily  dissolve  in  some  of 
the  other  liquids  mentioned.  Dry-cleaning  processes  make 
use  of  gasoline  instead  of  water  as  a  solvent  for  the  grease  and 
dirt.  When  alcohol  is  used  as  a  solvent,  the  resultant  solu- 
tion is  often  called  a  tincture.  In  general,  crystalline  sub- 
stances dissolve  more  readily  than  those  which  are  amorphous, 
but  there  are  many  exceptions  to  this  rule.  A  substance  that 
will  not  dissolve  in  a  given  liquid  is  said  to  be  insoluble  in  it. 
When  in  a  finely  divided  state,  many  insoluble  substances  will 
9  129 


130  EXPERIMENTAL   GENERAL    SCIENCE 

remain  in  the  liquid  for  a  long  time  before  settling  to  the  bot- 
tom.    In  such  cases  they  are  said  to  be  suspended  in  it. 

109.  Conditions  Affecting  Solution. — The  rapidity  with 
which  a  substance  goes  into  solution  depends  somewhat  upon 
its  temperature,  the  size  of  its  particles,  and  whether  the  sol- 
vent is  still  or  in  motion.  When  dissolving  a  solid,  warming 
the  solvent  not  only  causes  the  solid  to  dissolve  faster,  but 
increases  the  capacity  of  the  solvent  for  it,  just  as  we  have  seen 
that  heating  the  air  increases  its  capacity  for  moisture.  At 
zero  Centigrade,  100  grams  of  water  will  dissolve  13  grams  of 
saltpeter,  but  if  the  water  is  warme'd  to  20°C.,  it  will  then  dis- 
solve 32  grams.  Powdering  the  solid  to  be  dissolved  hastens 
the  process  since  it  increases  the  surface  which  comes  into 
contact  with  the  liquid.  Shaking  the  solvent  also  hastens  the 
process  since  it  removes  the  matter  already  dissolved  from 
the  vicinity  of  the  solute  and  allows  more  to  be  dissolved. 
Although  warming  the  liquid  usually  increases  its  capacity  for 
solids,  it  has  the  opposite  effect  on  its  capacity  for  gases.  When 
the  temperature  of  the  liquid  containing  the  gas  is  increased, 
the  gas  at  once  tends  to  escape.  This  is  seen  in  a  glass  of 
water  left  standing  in  a  warm  room  for  a  time,  the  bubbles 
formed  on  the  sides  of  the  glass  being  the  gases  driven  out  as 
the  temperature  rose. 

110.  Strength  of  Solution. — The  strength  of  a  solution  de- 
pends upon  the  amount  of  the  solute  it  contains.  If  very  little 
is  present,  it  is  said  to  be  weak  or  dilute;  if  much  is  present,  it  is 
strong.  A  concentrated  solution  is  one  that  has  been  made  very 
strong,  often  by  evaporating  some  of  the  solvent.  A  solution 
that  has  all  of  the  solid  it  can  hold,  is  said  to  be  saturated.  If 
the  temperature  of  the  solution  is  now  increased  it  can  take 
up  more  of  the  solute,  but  if  the  temperature  is  lowered, 
its  capacity  is  decreased  and  some  of  the  solute  must  be 
dropped,  just  as  cooling  the  air  may  cause  it  to  drop  some  of  its 
moisture  as  rain.  If  the  liquid  containing  the  solid^evaporates, 


SOLUTIONS  131 

the  solvent  alone  disappears,  and  the  solute  remains  behind.  A 
few  solutions  may  be  cooled  below  the  saturation  point,  with- 
out causing  them  to  drop  any  of  the  solute.  Such  solutions  are 
said  to  be  super-saturated.  When  a  bit  of  the  solute  is  dropped 
into  such  a  solution,  however,  the  solution  at  once  throws 
down  the  extra  solute  and  returns  to  the  saturated  condition 
again. 

111.  Crystallization. — When  a  saturated  solution  is  allowed 
to  cool,  or  the  amount  of  the  solvent  is  reduced  by  evapora- 
tion or  otherwise,  particles  of  the  solute  begin  to  appear,  usu- 
ally in  definite  and  characteristic  forms  known  as  crystals.     A 
crystal,  once  formed,  may  go  on  increasing  in  size  by  the  addi- 
tion of  more  material,  but  it  always  maintains  its  character- 
istic form.     Snowflakes  are  crystals  of  water,  and  sugar  and 
salt  are  other  forms  of  crystals.     In  general,  the  slower  the 
process  of  crystallization  goes  on,  the  larger  the  crystals  are 
likely  to  be.     When  more  than  one  solute  is  found  in  a  solvent, 
each  tends  to  crystallize  out  by  itself. 

112.  Mineral  Waters. — Water,  as  it  falls  in  rain,  is  nearly 
pure,  but  when  it  sinks  into  the  soil,  it  begins  to  take  up  the 
soluble  materials  it  encounters  so  that  when  it  appears  again 
in  the  form  of  springs,  wells,  and  the  like,  it  usually  holds  con- 
siderable matter  in  solution.     In  many  parts  of  the  earth  are 
extensive  beds  of  salt,  iron,  gypsum  and  other  minerals  that 
have  been  carried  in  watery  solutions  to  the  places  in  which 
they  are  found,  and  left  as  the  water  evaporated.     When 
water  carries  enough  mineral  matter  in  solution  to  give  it  an 
appreciable  flavor,  it  is  called  a  mineral  water.     The  common- 
est substances  in  mineral  waters  are  salt,  soda,  iron,  sulphur, 
and  lime.     Waters  containing  considerable  potash  or  soda  are 
called  alkali  waters.     In  arid  regions,  the  water,  after  pene- 
trating the  soil  and  dissolving  out  some  of  the  soluble  alkalis, 
may  rise  to  the  surface  by  capillarity  and  evaporate,  leaving  the 
alkali  behind  and  thus  rendering  the  soil  unfit  for  cultivation. 


132  EXPERIMENTAL   GENERAL   SCIENCE 

113.  Hard  Water. — Hard  water  is  simply  water  carrying 
certain    mineral    compounds    in    solution.     The    substances 
usually  found  are  calcium  sulphate,   or  gypsum   (CaS04), 
magnesium  sulphate   (MgS04)   and   calcium   hydrogen  car- 
bonate (Ca  (HC 0)3)2),  which,  instead  of  producing  an  agreeable 
lather  with  soap,  form  a  scum  that  fails  to  cleanse.     It  is, 
therefore,  customary  to  add  borax,  ammonium  carbonate,  or 
washing  soda  which  combines  with  these  substances  and  thus 
" softens"   the   water.     Water   containing  calcium  hydrogen 
carbonate  is  said  to  be  temporarily  hard  because  it  can  be  soft- 
ened by  boiling,  or  by  adding  slaked  lime.     This  causes  the 
dissolved  material  to  settle  to  the  bottom.     In  steam  boilers 
when   hard   waters   are   used,   this   accumulation    forms    a 
" scale"  which  causes  much  trouble  by  preventing  the  proper 
heating    of    the    water.    Permanently    hard    water    contains 
calcium  sulphate  and  cannot  be  softened  by  boiling. 

114.  Diffusion. — If  a  lump  of  a  soluble  substance  be  dropped 
into  a  liquid,  it  will  ultimately  spread  evenly  through  it,  even 
if  the  liquid  is  not  stirred.     The  process  by  which  this  is  ac- 
complished is  known  as  diffusion.     A  liquid  may  dissolve  in  a 
liquid,  or  a  gas  dissolve  in  a  gas,  by  diffusion,  as  when  illumi- 
nating gas  escapes  from  leaking  pipes  and  spreads  through  a 
room,  or  as  water  vapor  disappears  in  air.     In  such  cases, 
either  gas  or  liquid  may  be  considered  as  the  solvent,  though 
it  is  customary  to  regard  the  one  present  in  the  larger  amount 
as  entitled  to  the  name.     When  a  weak  and  a  strong  solution 
of  the  same  kind  come  into  contact,  they  also  mix  by  diffusion. 

115.  Other  Forms  of  Solutions. — While  the  disappearance 
of  a  solid  in  a  liquid  is  the  most  familiar  form  of  solution,  there 
are  various  other  associations  of  substances  that  are  fairly 
included  under  the  title.     Gases  as  well  as  solids  may  be  dis- 
solved in  liquids.     The  air  breathed  by  fishes  and  other  aquatic 
animals  is  thus  dissolved  in  the  water.     Gases  may  even  be 
dissolved  in  solids.     Charcoal   will  take  up  in  this  way  40 


SOLUTIONS  133 

times  its  volume  of  carbon  dioxide  and  90  times  its  volume 
of  ammonia.  It  has  such  an  affinity  for  bromine  gas  that  if 
a  piece  of  it  is  dropped  into  a  jar  of  this  gas,  it  will  absorb  it  so 
strongly  as  to  produce  a  vacuum  in  the  jar.  Under  proper 
conditions,  charcoal  may  be  made  to  absorb  the  air  from  a 
vessel,  making  a  more  perfect  vacuum  than  can  be  obtained 
by  the  best  air  pumps.  The  rare  metal  palladium  will  take 
up  800  times  its  volume  of  hydrogen,  and  spongy  platinum 
absorbs  th  s  gas  so  rapidly  that  the  striking  of  the  molecules 
against  it,  soon  generates  enough  heat  to  raise  the  gas  to  the 
kindling  temperature.  Self-lighting  gas  mantles  are  con- 
structed on  this  principle.  Solids  are  said  to  hold  gases  by 
occlusion.  Water  may  also  be  dissolved  in  solids  and  is  then 
known  as  water  of  crystallization.  When  gypsum  and  certain 
other  minerals  are  heated,  this  water  is  given  off,  but  the  crys- 
talline structure  is  thereby  destroyed,  and  the  substance  be- 
comes a  powder.  Plaster  t)f  Paris  is  made  by  driving  the  water 
of  crystallization  out  of  gypsum. 

116.  Alloys. — Homogeneous  mixtures  of  metals  are  called 
alloys,  but  in  a  way  these  are  also  solutions.  In  making  alloys, 
the  metals  are  usually  brought  to  the  liquid  state,  though  they 
may  slowly  mix  even  when  solid.  If  gold  is  placed  in  close 
contact  with  lead  and  left  for  a  time,  particles  of  it  may  be 
found  in  the  lead.  Gold  readily  dissolves  in  mercury,  forming 
a  true  solution.  When  working  with  mercury,  care  must  be 
taken  not  to  get  it  on  gold  rings  and  the  like.  A  large  number 
of  alloys  have  important  uses.  Brass  is  a  mixture  of  copper 
and  zinc.  Bronze  consists  mostly  of  copper,  tin  and  zinc. 
German  silver  is  made  of  copper,  nickel,  and  zinc  and  has  no 
silver  in  it.  Type  metal  is  composed  of  lead,  tin,  and  antimony. 
Alloys  very  frequently  have  melting  points  far  below  the  melt- 
ing points  of  the  individual  metals  composing  them.  Fusible 
metals  used  as  plugs  for  automatic  fire  extinguishers  and  the 
like  are  made  of  various  mixtures  of  lead,  antimony,  tin,  bis- 


134  EXPERIMENTAL   GENERAL   SCIENCE 

muth,  and  cadmium.  Alloys  containing  mercury  are  called 
amalgams,  and  are  frequently  used  by  dentists.  Our  silver 
and  gold  coins  always  contain  a  certain  amount  of  copper  for 
the  purpose  of  making  them  harder.  Pure  gold  is  said  to  be 
24  carats  fine.  This  is  much  too  soft  for  use  in  ornaments  and 
the  like.  Eighteen-carat  or  14-carat  gold  is  commonly  used. 
Zinc,  tin,  and  aluminum  are  insoluble  in  most  liquids,  which 
explains  their  use  in  cooking  utensils  and  other  vessels. 

117.  Solution  and  Change  of  State. — Practically  all  liquids 
have  definite  temperature  points  at  which,  when  pure,  they 
assume  gaseous  and  solid  conditions.     When  a  solid  is  dis- 
solved in  a  liquid,  however,  it  usually  affects  both  its  boiling 
and  freezing  points,  spreading  them  apart  as  it  were,  by  raising 
the  boiling  point  and  lowering  the  freezing  point.     Boiling 
syrup  may  be  made  much  hotter  than  boiling  water,  while 
brine,  made  of  table  salt  (sodium  chloride)  and  water,  may  be 
cooled  to  22°  below  zero  Centigrade  before  it  becomes  solid. 
By  the  use  of  another  salt,  calcium  chloride,  a  brine  may  be 
made  which  does  not  freeze  until  the  temperature  reaches  55° 
below  zero  Centigrade.     When  a  liquid  is  boiling,  dissolving 
a  solid  in  it  will  reduce  its  temperature  for  the  reason  that,  in 
dissolving,  the  molecules  of  the  solid  are  spread  much  farther 
apart,  and  the  heat  necessary  for  this  is  absorbed  from  the 
liquid.     Salt  in  contact  with  ice  dissolves  in  the  water  from 
the  melting  ice  and,  absorbing  heat  in  the  process,  forms  a 
brine  that  does  not  freeze  until  a  much  lower  temperature  is 
reached.     The  heat  given  out  by  the  brine,  as  its  temperature 
lowers,  goes  to  melt  more  ice.     This  explains  the  custom  of 
putting  salt  on  icy  sidewalks  and  car  tracks  in  winter.     In  the 
ice  cream  freezer,  the  cold  brine  absorbs  heat  from  the  cream. 
In  making  a  freezing  mixture  of  this  kind,  one  part  salt_and 
three  parts  ice  is  about  the  right  proportion. 

118.  Emulsions. — Emulsions  are  not  true  solutions,   but 
since  they  consist  of  substances  in  close  association,  they  may 


SOLUTIONS  135 

be  mentioned  here.  Emulsions  may  be  defined  as  two  sub- 
stances that  will  not  mix  without  the  addition  of  a  third.  One 
of  the  substances  is  usually  a  fat  or  an  oil.  The  kerosene 
emulsion  frequently  used  to  kill  insects  on  plants  is  made  of 
kerosene  and  water  to  which  is  added  a  quantity  of  soap. 
Kerosene  and  water  will  not  mix,  but  the  soap  causes  them  to 
form  an  emulsion.  The  ingredients  in  emulsions  are  likely  to 
separate  out  if  left  standing  for  some  time,  but  readily  mix 
again  when  well  shaken. 

Practical  Exercises 

1.  Put  a  small  quantity  of  clay  in  one  test-tube  and  a  crystal  of  potas- 
sium permanganate  in  another.     Fill  each  half  full  of  water  and  shake 
thoroughly.     In  which  tube  is  the  matter  suspended  and  in  which 
dissolved? 

2.  Is  a  solution  necessarily  colorless? 

3.  How  do  you  explain  the  fact  that  some  substances,  which  will 
not  dissolve  in  a  cold  liquid,  will  dissolve  when  the  liquid  is  heated? 

4.  When  streams  are  muddy  after  a  rain,  is  the  material  dissolved  or 
suspended  in  the  water? 

5.  Why  is  the  sea  salt,  if  all  the  rivers  that  run  into  it  appear  to  be 
fresh? 

6.  Explain  how  water  may  form  caves. 


7.  In  caves,  stalactites    (long  points  of  stone,  like  icicles)  are  often 
formed  by  water  containing  mineral  matter  which  seeps  through  the 
roof.     Explain  how  the  water  evaporating  may  form  these  objects. 

8.  Which  do  you  consider  the  better  bluing  for  laundry  purposes,  one 
that  is  dissolved  in  the  water  or  one  that  is  suspended  in  it? 


136  EXPERIMENTAL   GENERAL   SCIENCE 

9.  Why  is  the  water  in  shallow  wells,  especially  in  cities,  usually  unfit 
to  drink? 

10.  Explain  how  coffee  is  made  by  pouring  hot  water  over  the  coffee 
in  a  percolator. 

11.  Make  a  saturated  solution  of  nitrate  of  soda  or  sal  ammoniac  and 
water  and  put  a  few  drops  on  a  clean  sheet  of  glass,  draining  off  all  that 
does  not  cling  to  the  glass.     What  happens  to  the  solute  as  the  solvent 
evaporates? 

12.  With  a  simple  lens,  examine  the  material  left  on  the  glass.     What 
is  the  shape  of  the  crystals? 


13.  Make  a  dilute  solution  of  table  salt  and  water  and  place  in  a 
broad  flat  dish  to  evaporate.     How  does  the  shape  of  the  salt  crystals 
compare  with  those  made  in  the  previous  experiment? 

14.  How  do  you  account  for  the  diffusion  of  gases  by  the  molecular 
theory  of  matter? 

15.  Heat  some  ammonia  water  in  a  florence  flask  stopped  with  a  one- 
hole  stopper  through  which  is  thrust  a  glass  tube.     Hold  a  test-tube 
over  the  end  of  the  glass  tube  and  catch  some  of  the  ammonia  gas 
driven  off.     When  the  tube  is  full,  plunge  it,  mouth  down,  into  a  dish  of 
water.     Explain  the  disappearance  of  the  gas. 

16.  Could  aquatic  animals  live  in  water  that  had  first  been  boiled  and 
then  cooled?    Why? 

17.  The  "flat"  taste  of  boiled  water  may  be  removed  by  exposing  the 
water  to  the  air  for  a  time,  or  by  shaking  it  up  in  a  jar  with  air.     Explain. 

18.  Carbonated  water,  such  as  is  used  at  soda  fountains,  consists  of 
carbon  dioxide  in  solution  in  the  water.     Should  the  water  be  hot  or 
cold  to  take  up  as  much  carbon  dioxide  as  possible? 


SOLUTIONS  137 

19.  Account  for  the  lack  of  pungency  or  "bite"  in  a  glass  of  carbonated 
water  that  has  stood  for  some  time  exposed  to  the  air. 

20.  Household  ammonia  consists  of  ammonia  gas  dissolved  in  water. 
When  is  the  cork  likelier  to  pop  out  of  the  ammonia  bottle,  on  a  cold  or 
on  a  warm  day?     Why? 

21.  How  does  adding  more  of  a  solute  affect  the  density  of  a  solution? 


22.  Which  would  freeze  earlier  in  winter,  a  shallow  lake  or  an  equally 
shallow  inlet  from  the  ocean?     Why? 


23.  Why  does  salting  boiling  water  stop  the  boiling  for  a  short  time? 

24.  Suppose  that  on  a  cool  night,  ice  should  form  (crystallize)  on  a 
quantity  of  vinegar  or  sugar  and  water.     Do  you  infer  that  the  remainder 
of  the  solution  would  be  weaker  or  stronger  than  before?     Why? 

25.  Water  is  often  said  to  "purify  itself"  by  freezing.     Explain. 


26.  When  the  sea  in  the  arctic  regions  freezes,  which  do  you  infer 
contains  the  more  salt,  the  water  or  the  ice? 

27.  What  can  you  say  of  the  seriousness  of  burns  from  boiling  syrup 
and  the  like? 


28.  Does  putting  sugar  in  your  coffee,  cool  or  warm  it? 

29.  Why,  in  fixing  the  boiling  point  on  the  thermometer,  must  pure 
water  be  used? 

30.  Explain  the  use  of  charcoal  in  deodorizing  sick  rooms. 

31.  Milk,  butter,  and  other  foods  left  near  strong-smelling  substances 
will  take  up  their  odors.    Explain  how  this  occurs. 


138  EXPERIMENTAL   GENERAL   SCIENCE 

32.  In  making  certain  kinds  of  perfumes,  fresh  flowers  are  placed  in 
closed  vessels  whose  walls  are  covered  with  a  layer  of  lard  or  other  fat. 
Later  the  perfume  is  found  in  the  fats.    How  did  it  get  there? 

33.  Place  a  crystal  of  copper  sulphate  in  a  test-tube  and  heat  slowly. 
Explain  the  source  of  the  substance  that  forms  on  the  cooler  part  of  the 
tube. 


34.  In  making  alloys,  how  does  melting  the  metals  form  an  alloy 
more  rapidly  than  if  the  two  solids  were  placed  together? 


35.  Milk  is  a  natural  emulsion.     Can  you  discover  what  substance  in 
the  milk  corresponds  to  the  kerosene  in  kerosene  emulsion? 

36.  How  dp  soap  and  water  aid  in  taking  grease  out  of  clothing? 

37.  Cleaning  fluid  is  usually  made  of  several  fluids  mixed  together. 
Why  is  this? 


CHAPTER  XX 
PRECIPITATION,  FILTRATION,  AND  DISTILLATION 

119.  Precipitates. — When    two    liquids    are    poured    to- 
gether, one  usually  dissolves  in  the  other,  unless  they  happen 
to  be  liquids  that  never  mix,  such  as  oil  and  water,  but  in 
certain  cases,  two  liquids,  instead  of  forming  a  solution,  make 
new  chemical  combinations  some  of  which  are  not  soluble. 
In  such  cases,  the  insoluble  matter  soon  sinks  to  the  bottom. 
Matter  thrown  out  of  a  solution  in  this  way  is  called  a  precipi- 
tate.    Water  and  alcohol  readily  mix,  but  when  alcohol  has 
camphor  dissolved  in  it,  the  addition  of  water  forces  the 
camphor  out  of  the  combination  and  causes  it  to  appear  in 
the  mixture  as  small  white  flakes.     If  the  matter  suspended 
in  a  liquid  is  so  finely  divided  as  to  settle  very  slowly,  adding 
other  substances  to  it  may  cause  the  particles  to  come  together 
into   larger   groups  and  settle  more  rapidly.     This  process 
is  known  as  flocculation.     Iron  sulphate  and  alum  are  sub- 
stances often  used  in  clearing  turbid  water  by  flocculation. 
Lime  added  to  water  in  which  clay  is  suspended  will  also  cause 
flocculation.     The  particles  in  clay  soils  may  be  flocculated 
in  the  same  way. 

120.  Filters  and  Filtering. — A  precipitate  may  be  separated 
from  the  liquid  containing  it  by  passing   it   through   sub- 
stances containing  many  fine  pores.     Such  substances  are 
known  as  filters.     In  the  laboratory,  filters  are  usually  made 
of  a  special  paper,  called  filter  paper,  but  other  filters  may  be 
made  of  charcoal,  glass  wool,  stone,  beds  of  sand,  and  the  like. 
Only  precipitates,  or  suspended  matter,  can  be  separated  from 

139 


140 


EXPERIMENTAL   GENERAL   SCIENCE 


the  liquid  by  filtration,  matter  in  solution  passing  through 
unchanged.  In  many  cities,  the  water  for  household  use  is 
filtered  through  beds  of  sand.  This  gives  clear  water,  but  not 
necessarily  pure  water,  since  it  does  not  remove  dissolved 
matter. 

121.  Distillation. — When  it  is  desired  to  recover  the  solid 
matter  in  a  solution,  this  is  easily  accomplished  by  evaporating 
the  solvent.  The  solvent  may  also  be  obtained  in  its  original 


FIG.  46. — Apparatus  used  in  filtering.     (Rockwood.) 

state  by  catching  the  vapor  as  it  rises,  and  cooling  it  to  the 
liquid  state  again.  The  latter  process  is  called  distillation. 
The  distilling  apparatus  consists  essentially  of  a  closed  vessel 
in  which  the  matter  to  be  distilled  is  heated,  with  a  coil  of 
pipe  for  cooling  and  condensing  the  vapor  produced.  The 
coil  of  pipe,  often  called  the  "worm,"  may  be  kept  cool  by 
being  immersed  in  a  tank  or  stream  of  running  water.  The 
condensed  vapor  which  slowly  drops  from  the  coil  of  pipe, 


PRECIPITATION,    FILTRATION,   AND   DISTILLATION        141 

is  called  the  distillate.  For  purposes  of  illustration,  liquids 
may  be  distilled  in  a  florence  flask  closed  by  a  stopper  through 
which  extends  a  glass  tube.  The  vapor  driven  off  through  the 


FIG.  47. — How  to  fold  a  filter  paper. 

tube  may  be  condensed  by  being  directed  against  a  bottle  of 
cold  water  or  caught  in  a  test-tube  immersed  in  water.  A 
large  number  of  the  fragrant  oils  used  in  medicine  and  the  arts 


48. — Apparatus  for  distilling  in  the  laboratory. 
Turton.) 


(Tower,  Smith  and 


are  obtained  by  distillation.  In  the  same  way,  alcohol  is 
derived  from  liquids  containing  it.  When  liquids  with  dif- 
ferent boiling  points  are  mixed  together,  they  may  be  recovered 
separately  by  regulating  the  temperature  of  the  mixture.  The 


142 


EXPERIMENTAL    GENERAL   SCIENCE 


liquid  with  the  lowest  boiling  point  would  come  off  first,  fol- 
lowed by  others  in  the  order  of  their  boiling  points,  as  the  tem- 
perature is  increased.  This  is  called  fractional  distillation. 
Naphtha,  benzine,  gasoline,  kerosene,  coke,  and  a  large  number 
of  other  substances  are  obtained  from  crude  petroleum  by  this 
process.  Occasionally  solids  may  be  broken  down,  by  means 
of  heat,  into  one  or  more  new  products,  gaseous,  liquid,  or 
solid.  This  is  called  dry  or  destructive  distillation.  By  this 


A 

V\ 


FIG.  49. — Distillation  of  coal  in  test-tube. 


means  wood  alcohol,  acetic  acid,  and  charcoal  are  derived  from 
various  hard  woods,  and  coal  is  made  to  produce  coke,  tar, 
illuminating  gas,  and  other  substances.  From  the  coal  tar  are 
also  derived  a  large  number  of  useful  products  among  which  are* 
numerous  dyes.  The  wood  alcohol  obtained  by  dry  distilla- 
tion of  wood,  differs  from  ordinary  alcohol  in  being  very 
poisonous.  Denatured  alcohol  is  ordinary  or  grain  alcohol 
to  which  has  been  added  a  small  quantity  of  wood  alcohol  or 
other  substance  to  render  it  unfit  for  internal  use. 


PRECIPITATION,    FILTRATION,    AND   DISTILLATION         143 

Practical  Exercises 

1.  Make  a  solution  of  about  one-half  gram  of  lead  nitrate  in  10  cubic 
centimeters  of  distilled  water.  To  this  solution  add  an  equal  volume  of 
salt  water.  What  happens  when  the  two  solutions  are  mixed? 


2.  What  term  describes  the  matter  you  now  have  in  the  bottom  of  the 
test-tube? 


3.  Place  a  filter  paper  in  a  glass  funnel  supported  by  a  ring  stand 
and  pour  the  mixture  you  have  made  into  it,  catching  the  filtered  liquid 
in  a  beaker.  What  part  of  the  mixture  fails  to  pass  through  the  filter? 


4.  Dissolve  some  salt  in  water  and  filter  through  a  clean  filter  paper. 
Taste  the  liquid  that  filters  through.     Does  the  salt  filter  out?     Why? 


6.  Shake  up  a  crystal  of  potassium  permanganate  in  a  test-tube  and 
filter.  Was  this  substance  dissolved  in  the  water  or  merely  held  in 
suspension? 


6.  How  could  you  separate  a  mixture  of  salt  and  sand? 

7.  How  could  you  separate  a  mixture  of  salt  and  water? 

8.  In  sugar  making,  the  syrup  is  clarified  and  its  color  removed  by 
being  passed  through  bone-black,  a  charcoal  made  from  bones.     Explain 
how  the  syrup  can  be  clarified  in  this  way. 


9.  Filters  for  home  use  are  often  made  of  a  layer  of  charcoal,  others 
have  a  bottom  of  fine  porous  stone  through  which  water  filters.  What 
do  you  infer  as  to  the  need  for  frequently  cleaning  such  niters? 


10.  Cisterns  are  often  divided  by  a  brick  wall,  the  rain  water  coming 
in  on  one  side  of  the  wall  and  the  house  supply  being  pumped  away 
from  the  other.  Of  what  advantage  is  this? 


144  EXPERIMENTAL   GENERAL   SCIENCE 

11.  If  alcohol  and  water  were  mixed  together,  which  would  be  driven 
off  first  when  heat  was  applied? 

12.  Sea  water  is  unfit  to  drink  because  of  various  salts  dissolved  in 
it.     Can  you  suggest  a  method  of  obtaining  pure  water  from  sea  water? 

13.  Put  about  a  spoonful  of  powdered  soft  coal  into  a  test-tube,  cork 
with  a  one-hole  stopper  containing  a  glass  tube.     Apply  heat  from  the 
bunsen  burner.     What  is  given  off  through  the  glass  tube? 

14.  Will  this  substance  burn? 

16.  What  form  of  distillation  is  illustrated  by  the  preceding  experiment  ? 

16.  Turpentine  is  obtained  from  the  pitch  of  various  pine  trees  which 
is  heated  with  water.     The  volatile  turpentine  is  driven  off  and  resin  or 
rosin  is  left.     What  phase  of  distillation  does  this  illustrate? 

17.  In  many  chemical  experiments,  it  is  necessary  to  use  distilled 
water.     Why  not  use  ordinary  water? 


CHAPTER  XXI 
ACIDS,  BASES  AND  SALTS 

122.  Nature  of  Acids. — The  most  characteristic  thing  about 
acids  is  their  sour  taste.     In  addition,  they  have  the  peculiar 
property  of  turning  certain  vegetable  juices  red  or  pink.     Blue 
flowers  often  become  pink  in  the  presence  of  dilute  acids,  and 
the  change  from  pink  buds  to  blue  flowers  is  frequently  due  to 
the  change  in  the  acid  contents  of  the  cells.     The  familiar  test 
for  acids  is  litmus  paper,  made  by  soaking  paper  in  a  solution 
derived  from  a  kind  of  plant  called  a  lichen.     All  acids  redden 
blue  litmus  paper.     Another  test  for  acids  is  to  add  them  to 
carbonates,  such  as  limestone  or  baking  soda.     With  such  sub- 
stances, they  produce  a  bubbling  or  effervescence,  due  to  the 
carbon  dioxide  released.     All  acids  contain  hydrogen  and  all 
dissolve    in    water.     Acids    are    very    generally    distributed 
throughout  the  plant  and  animal  kingdom.     Among  the  com- 
monest, are  malic  acid  found  in  apples,  citric  acid  in  lemons, 
acetic  acid  in  vinegar,  tartaric  acid  in  grapes,  oxalic  acid  in 
rhubarb,  lactic  acid  in  sauerkraut  and  sour  milk,  hydrochloric 
acid  in  the  stomach  of  many  animals,  and  carbonic  acid  in  the 
bodies  of  both  animals  and  plants.     Certain  other  acids  are 
sometimes  known  as  mineral  acids.     Among  these  are  nitric, 
sulphuric,  phosphoric,  and  hydrochloric  acids.     The  last  named 
is  commonly  known  as  muriatic  acid. 

123.  Bases. — In  many  ways,   bases  are  the  opposites  of 
acids.     This  is  especially  true  of  their  reaction  with  litmus 
paper,  since  they  turn  red  litmus  paper  blue.     Instead  of  being 
sour,  they  usually  have  a  bitter  taste,  and,  when  dissolved  in 

10  145 


146  EXPERIMENTAL   GENERAL   SCIENCE 

water  and  rubbed  through  the  fingers,  have  a  slimy  feel.  Most 
bases  consist  of  a  metal  combined  with  oxygen  and  hydrogen. 
Lime-water  and  ammonia  are  good  examples  of  bases.  When 
a  base  is  added  to  a  solution  of  phenolphthalin  it  is  turned  a 
bright  scarlet,  but  the  solution  becomes  colorless  again  when 
sufficient  acid  is  added.  A  strong  base  is  called  an  alkali. 
Caustic  potash  (potassium  hydroxide)  and  caustic  soda 
(sodium  hydroxide)  are  two  other  active  bases  which  are 
usually  known  as  lyes.  Both  acids  and  bases  attack  other 
substances  and  corrode  them. 

124.  Formation  of  Salts. — If  an  acid  be  added  drop  by  drop 
to  a  base,  a  mixture  may  be  formed  which  will  not  affect  either 
red  or  blue  litmus  paper,  and  which  is  not  corrosive  in  its 
action.  Such  a  solution  is  said  to  be  neutral.  When  a  base 
and  an  acid  neutralize  each  other  in  this  way,  a  chemical 
reaction  takes  place  which  results  in  the  formation  of  a  salt,  in 
addition  to  more  or  less  water.  Common  table  salt  (sodium 
chloride)  is  a  familiar  example  of  a  salt,  and  among  others  with 
which  we  are  familiar  may  be  mentioned  calcium  chloride, 
sodium  nitrate,  and  calcium  sulphate.  If  a  mixture  is  not 
quite  neutral,  we  may  have  an  acid  salt  or  a  basic  salt  accord- 
ing to  whether  the  base  or  acid  predominates.  Baking  soda  is 
a  basic  salt  and  therefore  affects  litmus  paper  like  a  base. 
Soaps  are  really  mixtures  of  salts.  When  a  potash  base  is 
used,  "soft"  or  liquid  soap  is  formed.  A  soda  base  is  used  for 
the  hard  soap  commonly  sold.  Soft  soap  may  be  made  hard 
by  the  addition  of  table  salt  during  the  process  of  manufac- 
ture. Laundry  soaps  usually  have  an  excess  of  alkali  which 
renders  them  unfit  for  toilet  use. 

Practical  Exercises 

1.  Test  the  substances  in  the  following  list  with  litmus  paper  and 
decide  which  react  as  acids  and  which  as  bases.  Those  that  are  not 
liquid  should  be  dissolved  in  a  little  water  before  testing: 


ACIDS,   BASES   AND    SALTS  147 

Borax  Molasses 

Cream  of  tartar  Lime-water 

Your  saliva  Baking  soda 

2.  Place  about  10  cubic  centimeters  of  sodium  hydroxide  (NaOH)  in 
an  evaporating  dish.     Is  it  an  acid  or  a  base? 


3.  Add  hydrochloric  acid,  drop  by  drop,  to  the  sodium  hydroxide, 
testing  after  each  addition  of  acid  until  the  solution  is  neutral.  Be 
careful  not  to  add  too  much  acid.  Evaporate  the  liquid,  taste  and  name 
the  substance  left  in  the  dish. 


4.  Write  the  chemical  formulas  for  the  acid  and  base  used  in  the 
preceding  experiment  and  cross  out  the  chemical  elements  found  in  the 
salt.  Can  you  tell  from  the  remainder,  what  the  liquid  was  that  you 
evaporated  ? 

6.  Baking  soda  is  often  added  to  sour  milk  to  "sweeten"  it,  that  is, 
to  remove  the  sour  taste.  Explain  how  this  is  accomplished. 


6.  The  pain  from  insect  stings  is  usually  due  to  formic  acid  introduced 
into  the  wound.     Why  does  the  application  of  ammonia  reduce  the  pain? 


7.  Strong  acids  rapidly  destroy  the  skin,  clothing,  and  other  sub- 
stances. If  one  spilled  acid  on  hands  or  clothing,  what  could  be  used  to 
render  the  acid  harmless? 


8.  Burns  produce  an  acid  condition  of  the  flesh.    Why  apply  lime- 
water? 


9.  Soils  sometimes  become  sour  through  the  accumulation  in  them 
of  acids  derived  from  decaying  vegetation.  Why  will  limestone  added 
to  such  soils  "sweeten"  them. 


10.  Soda  mints  consist  largely  of  baking  soda.     Why  may  they  be 
taken  to  correct  sour  stomach  ? 


148  EXPERIMENTAL   GENERAL   SCIENCE 

11.  In  baking,  cream  of  tartar  and  baking  soda  are  often  mixed 
together  and  these,  in  the  presence  of  moisture  effervesce  and  give  off 
much  carbon  dioxide.     It  is  this  gas,  increased  in  volume  by  the  heat 
of  baking,  that  causes  cake,  biscuit,  and  the  like  to  rise.     When  sour 
milk  is  used  in  baking,  cream  of  tartar  may  be  omitted,  but  not  the 
soda.     Why? 

12.  When  molasses  is  used  in  baking,  the  addition  of  soda  alone  will 
make  the  cake  light.     What  substance  do  you  infer  must  be  present  in 
the  molasses? 


13.  All  baking  powders  are  mixtures  of  an  acid  and  a  carbonate,  the 
latter  a  salt  of  carbonic  acid  and  sodium.     Usually  a  small  quantity  of 
corn  starch  is  added  to  keep  them  apart.     Why  do  they  not  give  off  their 
contained  carbon  dioxide  if  the  can  is  kept  closed? 

14.  If  baking  powder  is  left  exposed  to  the  air,  it  deteriorates.     Why? 

15.  Why  are  baking  powders  always  stirred  into  the  flour  before 
moisture  is  added? 


CHAPTER  XXII 
LIGHT  AND  VISION 

125.  Radiation  from  Luminous  Bodies. — When  a  body  is 
heated  very  hot,  it  gives  off,  in  addition  to  the  heat  rays,  cer- 
tain other  rays  which  have  the  power  of  affecting  the  retina 
of  the  eye,  thus  producing  a  sensation  which  we  know  as  light. 
All  bodies  which  give  out  light  rays  are  said  to  be  luminous. 
The  sun  is  a  luminous  body,  and  so  are  the  stars,  but  the  moon 
is  not  because  it  shines  by  reflected  sunlight.  From  the  fact 
that  light  passes  easily  across  space  in  which  there  is  no  matter 
of  any  kind,  we  perceive  that  the  light  waves  are  not  waves  in 
air.  Scientists  regard  them  as  waves  in  a  mysterious  sub- 
stance called  ether,  about  which  practically  nothing  is  known, 
but  which  is  supposed  to  exist  between  the  molecules  of  matter 
as  well  as  between  the  earth  and  the  other  heavenly  bodies. 
Though  it  is  almost  impossible  to  study  the  ether,  the  waves 
that  occur  in  it,  that  is,  the  heat  and  light  waves,  are  very  well 
known.  The  number  and  direction  of  their  vibrations  have 
been  ascertained  and  their  speed  has  been  accurately  measured 
and  found  to  be  about  186,000  miles  a  second.  Such  a  veloc- 
ity is  inconceivable.  For  all  distances  on  the  earth,  it  is  prac- 
tically instantaneous.  In  passing  from  the  sun  to  the  earth, 
however,  the  distance  is  so  great  that  about  eight  minutes  are 
required.  We  know  that  light  travels  in  a  straight  line,  be- 
cause all  opaque  bodies  cast  shadows  which  have  the  same 
outlines  as  the  bodies  themselves.  Moreover,  when  light 
enters  a  dark  room  through  some  small  opening,  we  find  it 
always  follows  a  straight  path,  as  is  shown  by  the  fact  that 

149 


150 


EXPERIMENTAL   GENERAL   SCIENCE 


the  objects  it  strikes  are  always  in  line  with  the  source  of  light 
and  the  opening  through  which  it  comes. 

126.  Reflection  of  Light. — Though  light  travels  in  straight 
lines,  it  may  be  easily  diverted  or  reflected.  A  sunbeam  may 
be  caught  on  a  mirror  and  turned  completely  out  of  its 
course.  By  a  suitable  arrangement  of  mirrors,  its  course 
may  be  changed  again  and  again.  Were  it  not  for  the  fact 
that  the  direction  of  rays  of  light  can  be  altered,  our  eyes 
would  be  of  little  use  to  us,  for  most  of  our  seeing  is  not  by 
direct  light,  but  by  light  which  has  first  fallen  on  some  object 


FIG.  50. — Angle  of  incidence  is  equal  to  angle  of  reflection. 

and  by  it  has  been  reflected  to  the  eye.  More  than  this, 
unless  the  object  viewed  is  in  direct  sunlight,  or  in  the  light 
from  some  other  source  of  illumination,  the  light  preceding 
from  it  has  been  diverted  more  than  once  before  it  reaches 
the  eye.  Rooms  into  which  the  sun  does  not  shine  during 
the  day  are  lighted  by  reflection  from  the  clouds,  from  dust 
in  the  air,  from  trees,  buildings,  and  similar  objects.  Smooth 
surfaces  are  the  best  reflectors  because  they  turn  back  the  light 
uniformly.  Objects  with  rough  surfaces  reflect  the  light  in 
many  directions,  each  small  irregularity  acting  as  a  separate 
mirror,  and  thus  a  clear  image  is  impossible.  Whenever  light 


LIGHT   AND   VISION 


151 


is  reflected,  it  is  important  to  observe  that  it  always  leaves 
the  reflecting  surface  at  the  same  angle  as  that  at  which  it 
falls  upon  it.  If  we  wish  to  see  ourselves  in  a  mirror,  we  must 
stand  squarely  in  front  of  it.  If  we  stand  a  little  to  one  side, 
we  perceive  only  objects  situated  at  the  same  angle  to  the 
mirror  on  the  opposite  side.  The  scientific  statement  of  the 
fact  is  that  "the  angle  of  reflection  equals  the  angle  of  inci- 
dence." The  principle  is  exactly  illustrated  in  bouncing  a 
ball  on  the  ground.  If  it  strikes  the  earth  at  an  angle,  it 
bounces  up  and  away  at  the  same  angle. 

127.  Refraction. — A  ray  of  light  may  be  turned  out  of  its 
course  in  passing  through  a  medium  as  well  as  when  reflected 


A   Y7 


FIG.  51,  —  A  prism  changes  the  direction 
of  a  ray  of  light. 


FIG.    52.  —  Cross-sections     of, 
convex  and  concave  lenses. 


from  its  surface.  The  turning  occurs  at  the  point  where  the 
light  passes  from  one  medium  into  another  of  different  density, 
as  from  air  to  water,  or  from  water  to  glass.  If  the  light 
strikes  the  surface  of  a  transparent  body  at  right  angles,  it 
goes  straight  through,  but  if  it  strikes  at  any  other  angle  it  is 
always  sent  out  of  its  course  in  the  direction  of  the  denser 
medium.  The  eye,  however,  is  not  cognizant  of  the  changing 
of  the  direction  of  the  light  rays,  and  sees  the  object  from  which 
the  light  is  reflected  exactly  as  if  the  rays  were  direct.  This 
often  results  in  curious  illusions;  in  fact,  the  eye  is  probably 
more  easily  deceived  than  any  of  our  other  senses. 


152 


EXPERIMENTAL   GENERAL   SCIENCE 


128.  Lenses. — Circular  pieces  of  glass  known  as  lenses,  by 
deflecting  the  light  rays  either  toward  or  away  from  one 
another,  make  objects  appear  to  be  larger  or  smaller  than  they 
really  are.  There  are  several  forms  of  lenses,  but  the  two 
most  frequently  used  are  the  double  convex  lens,  which  is  thick- 
est in  the  middle  and  curves  uniformly  to  the  edge,  and  the 

double  concave  lens,  which  is  just 
the  reverse  of  this.  When  rays 
of  light  pass  through  a  double 
convex  lens,  owing  to  the  curva- 
ture of  its  surfaces,  they  are 
directed  toward  the  thicker  part 

°^  ^ne  ^ens  anc^  made  to  fall  on  a 
single  spot,  or,  as  we  say,  are 


FIG.  53. — How  curvature  of 
the  lens  affects  direction  of  the 
light  rays.  (Tower,  Smith  and 
Turlon.) 


FIG.  54. — Bending  of  a  light  ray  by 
atmosphere;  sun  appears  to  be  higher 
than  it  really  is. 


brought  to  a  focus.  The  very  bright  spot  of  light  that 
appears  when  such  a  lens  is  held  a  short  distance  above  any 
convenient  surface  is  an  illustration  of  this  fact.  That  heat 
rays  as  well  as  light  rays  may  be  focused  is  well  known.  The 
double  convex  lens  is  sometimes  known  as  a  burning  glass  be- 
cause the  heat  rays  falling  on  it  may  set  fire  to  paper  when 
brought  to  a  focus.  When  light  from  an  object  passes  through 


LIGHT   AND   VISION 


153 


such  a  lens  and  falls  on  the  eye  at  the  proper  focus,  the  eye 
estimates  the  size  of  the  object  as  if  the  rays  come  straight 
from  it,  and  it  therefore  appears  to  be  larger,  or,  as  we  say,  it 
is  magnified.  The  double  concave  lens  is  often  called  a  dimin- 
ishing glass  because  objects  viewed  through  it  appear  smaller 
than  they  really  are,  due  to  the  spreading  of  the  light  rays. 
The  microscope  and  telescope  consist  essentially  of  two  sets  of 
lenses,  one  at  each  end  of  a  light-proof  tube.  The  set  nearer 
the  object  to  be  viewed  produces  a  magnified  image  of  it  within 
the  tube,  and  this  is  further  magnified  by  the  lenses  at  the 
opposite  end. 

129.  The  Camera. — The  camera  is 
essentially  a  light-proof  box  with  a  suit- 
able set  of  lenses  for  focusing  on  a  sen- 
sitive plate  or  film  the  light  rays  from  an 
object.  A  shutter  prevents  light  from 
entering  the  camera  until  the  picture  is 
to  be  made.  Then  a  very  short  exposure 
admits  sufficient  light  to  affect  the  emul- 
sion on  the  sensitized  plate  and  make  the 
picture.  In  this  picture,  or  negative,  the 
light  and  shade  of  nature  are  exactly  re- 
versed, since  light  objects  reflect  the  most 
light  into  the  camera  and  produce  the 
greatest  change  in,  or  darkening  of,  the  sensitized  surface. 
When  prints  are  made  from  negatives,  however,  the  darker 
parts  hold  back  the  light  more  than  others  and  thus  the  fin- 
ished photograph  reproduces  the  original  scene  in  its  proper 
lights  and  shades.  The  projection  lantern  or  stereopticon 
is  like  a  camera  reversed.  The  light  is  sent  through  a 
semi-transparent  slide  and  enlarged  by  a  suitable  set  of 
lenses  as  it  is  projected  on  the  screen.  The  eye  is  also  much 
like  the  camera.  The  cornea  and  crystalline  lens  focus  the 
rays  of  light  on  the  retina  or  sensitive  part  at  the  back  of  the 


FIG.  55. — Microscope. 


154  EXPERIMENTAL   GENERAL    SCIENCE 

eye,  and  the  iris,  like  the  opening  in  the  shutter,  can  be  enlarged 
or  diminished  to  admit  the  proper  amount  of  light.  In  our 
eyes,  a  continuous  picture  is  produced  as  long  as  the  eyes  are 
open,  and  no  shutter  to  keep  out  the  light  is  necessary,  though 
the  eyelids  may  function  like  shutters  on  occasion. 

130.  Persistence  of  Images. — When  an  image  is  formed  on 
the  retina,  it  does  not  vanish  instantly,  but  persists  for  about 
Ho  second.  A  glowing  stick  whirled  about  on  a  dark  night, 
therefore,  appears  like  a  fiery  circle  since  it  is  seen  in  several 
positions  in  a  short  space  of  time  and  the  images  overlap  as  it 
were.  It  is  this  peculiarity  of  the  eye  that  makes  moving 
pictures  possible.  A  series  of  pictures,  each  differing  slightly 


FIG.  56. — Formation  of  an  image  by  a  telescope,     b-a  is  the  real  image; 
d-c  is  the  virtual  image  seen  by  the  observer.    (Tower,  Smith  and  Turton.) 

from  the  one  which  precedes  it,  are  thrown  on  the  screen  and 
these,  reflected  to  the  retina,  blend  into  a  picture  in  which  the 
figures  seem  to  move.  The  eye  may  be  easily  deceived  in 
other  ways.  For  instance,  a  square  ruled  with  perpendicular 
lines  appears  to  be  shorter  than  one  ruled  with  horizontal 
lines. 

131.  Various  Effects  of  Light. — Since  light  is  a  form  of 
energy,  it  is  not  surprising  to  note  that  it  causes  numerous 
changes  in  matter  Most  of  these  effects  are  probably  chem- 
ical in  nature,  as  the  fading  of  colors,  the  tanning  of  the  skin, 
and  the  killing  of  germs.  Hydrogen  and  chlorine  mixed  in  the 
dark  are  inert  and  do  not  change,  but  if  a  ray  of  sunlight  strike 
them,  they  combine  with  explosive  violence.  Another  famil- 


LIGHT   AND   VISION 


155 


iar  instance  of  chemical  change  caused  by  light  is  the  decom- 
position of  matter  on  the  photographic  plate  when  the  picture 
is  made.  The  most  important  use  of  light  to  the  world  is  in 
supplying  the  energy  needed  by  all  plant  life,  and  (since  ani- 
mals are  entirely  dependent  on  plants)  of  all  animal  life  as 
well.  The  green  cells  of  plants  turn  the  light  energy  into 
electric  energy  and  by  its  aid  combine  the  materials  absorbed 
from  the  soil  and  air  into  food.  Plants  are  the  only  living 
things  that  can  thus  form  food  from  chemical  elements. 

132.  Phosphorescence. — A  large  number  of  substances  are 
now  known  which  have  the  power  of  storing  up  light  when 
exposed  to  the  sun's  rays,  and  of  giving  it  off  in  darkness.  Such 


FIG.  57. — Apparent  size  of  square  affected  by  direction  of  the  ruling. 

substances  are  said  to  be  phosphorescent.  In  all  cases  the  wave 
lengths  of  the  light  given  out  are  longer  than  those  taken  in. 
Some  substances  may  be  made  phosphorescent  by  friction, 
hammering,  or  splitting,  and  others  are  affected  by  electricity, 
heating,  etc.  Various  plants  give  out  rays  of  light  in  the  dark, 
and  a  large  number  of  the  lower  animals  also  have  this  power. 
The  fireflies  and  glowworms  are  good  illustrations.  The  phos- 
phorescence which  often  crests  the  waves  in  the  warmer  parts 
of  the  globe  is  caused  by  minute  one-celled  animals.  Lumi- 
nous paint  is  now  made  from  substances  which  are  strongly 
phosphorescent.  This  paint  absorbs  light  during  the  day  and 
emits  it  at  night,  and  is  therefore  of  value  for  covering  match- 
boxes and  other  objects  which  need  to  be  located  in  the  dark. 


156  EXPERIMENTAL   GENERAL   SCIENCE 

133.  Artificial  Lighting. — The  light  from  artificial  sources  of 
illumination  is  of  varying  intensity,  which  is  usually  expressed 
in  candlepower,  the  candlepower  being  defined  as  the  amount 
of  light  given  by  a  sperm  candle  burning  about  8  grams  of  wax 
an  hour.  In  lighting  our  dwellings  and  shops,  the  most  satis- 
factory light  is  that  which  comes  from  above  in  much  the  same 
way  that  the  light  from  the  sun  does.  Diffused  light  is  also 
better  than  direct  light.  One  should  avoid  too  much  light  on 
book  or  work  and  should  never  sit  facing  the  light.  In  our 
dwellings,  lights  are  commonly  surrounded  by  shades  designed 
to  reflect  the  light  in  many  directions  and  so  diffuse  it.  An- 
other method  of  securing  diffused  light  is  by  the  so-called 
indirect  lighting,  in  which  the  light  is  reflected  from  the  ceilings 
of  the  room.  Since  much  of  the  light  is  absorbed  by  the 
reflecting  surfaces,  this  is  an  expensive  though  very  desirable 
method  of  lighting. 

Practical  Exercises 

1.  Why  can  we  not  see  through  a  bent  tube  or  around  a  corner? 

2.  Can  you  think  of  a  way  of  making  objects  around  a  corner  visible? 

3.  Why  can  a  carpenter  tell  if  a  board  is  straight,  by  sighting  along  it? 

4.  Trace   the  rays  of  light  which  enable  you  to  see  yourself  in  a 
mirror. 

6.  Why  can  we  not  see  in  absolute  darkness? 

6.  What  makes  a  beam  of  light  visible  when  it  is  thrown  across  a 
dark  room? 

7.  Explain  the  appearance  of  "the  sun  drawing  water." 

8.  Why  does  it  not  become  dark  as  soon  as  the  sun  sets? 


LIGHT   AND   VISION  157 

9.  In  the  tropics,  twilight  is  much  shorter  than  in  temperate  regions, 
and  near  the  poles,  it  is  much  longer.  Why?  (What  part  of  the  earth 
turns  away  from  the  sun  most  rapidly?) 


10.  How  does  seeing  the  candle  flame  differ  from  seeing  the  candle? 

11.  Why  is  a  snowflake  or  ground  glass  white,  when  water  and  glass 
are  transparent? 


12.  Why  does  a  piece  of  white  cloth  or  a  light  soil  turn  darker  when 
wet? 


13.  How  does  frosted  or  roughened  glass  prevent  our  seeing  through  it? 


14.  Why  are  we  unable  to  see  out  of  the  window  after  the  lamps  are 
lighted? 


15.  How  does  painting  the  walls  of  cellars  and  other  dark  places  white 
increase  the  light  in  them? 


16.  Put  a  coin  in  a  moderately  deep  basin  and  stand  so  that  the  coin 
is  just  hidden  from  view  by  the  edge  of  the  vessel.  Let  a  classmate  slowly 
pour  water  into  the  basin  without  disturbing  the  coin.  How  does  this 
affect  your  seeing  it? 


17.  Explain  how  this  effect  was  produced, 


18.  Why  does  a  pole  projecting  from  the  water  appear  to  be  bent  at 
the  surface  of  the  water? 


19.  Put  a  spoon  in  a  glass  of  water  and,  looking  down  on  it,  place  your 
finger  on  the  outside  of  the  glass  at  the  point  where  the  spoon  seems 
to  touch  it.  How  does  this  compare  with  the  real  position  of  the  spoon? 


158  EXPERIMENTAL   GENERAL   SCIENCE 

20.  Would  you  say  that  ponds  are  deeper  or  shallower  than  they  appear 
to  be? 


21.  In  spearing  a  fish,  ought  one  to  aim  a  little  above  or  a  little  below 
it,  as  it  appears  in  the  water? 


22.  Recalling  the  different  densities  of  the  air  at  sea  level  and  at  high 
altitudes,  tell  whether  the  sun's  rays  are  bent  toward  or  away  from  the 
earth  at  sunrise  and  sunset? 


23.  Explain  how  we  can  see  the  sun  after  it  has  really  set,  or  before  it 
has  risen? 


24.  In  the  short-sighted  or  near-sighted  eye,  the  rays  of  light  come 
to  a  focus  before  reaching  the  retina.  Do  such  eyes  need  concave  or 
convex  glasses?  Why? 


26.  What  kind  of  glasses  should  the  far-sighted  eye  be  fitted  with 
if  in  such  eyes  the  light  does  not  come  to  a  focus  when  it  reaches  the 
retina? 


26.  Could  a  burning  lens  be  made  of  ice? 


27.  When  an  object  is  viewed  through  a  double  convex  lens,  why  is 
the  image  blurred  except  when  the  glass  is  held  at  a  definite  distance 
from  the  object? 


28.  By  means  of  a  mirror,  examine  the  pupil  of  your  eye  after  looking 
at  an  object  in  bright  light,  and  again  after  being  in  a  dim  light.     What 
effect  on  the  size  of  the  pupil  has  an  increase  or  decrease  in  the  amount 
of  light? 

29.  Would  you  expect  the  pupil  of  the  eye  to  be  expanded  or  contracted 
when  one  is  walking  at  dusk? 


LIGHT  AND   VISION  159 

30.  Why  do  owls  have  such  large  openings  in  the  iris? 

31.  Why  is  one  dazzled  when  brought  suddenly  from  darkness  into  a 
brightly  lighted  room? 

32.  Why  is  it  difficult  to  see  when  we  first  go  into  the  dark  from  a 
lighted  room. 

33.  On  a  dark  night,  one  is  able  to  see  fairly  well  after  he  has  been  in 
the  dark  for  some  time.     Why? 

34.  Why  are  cameras  always  painted  black  inside? 

35.  The  interior  of  the  ordinary  human  eye  is  black  but  albinos  lack 
this  pigment.     Albinos  cannot  see  well  in  bright  light.     Why? 

36.  Hold  a  pencil  a  few  inches  from  the  eye  and  look  at  some  point 
beyond  it,  first  with  one  eye  and  then  with  the  other.     What  advantage 
is  there  in  judging  distances,  size,  and  shape  in  having  two  eyes? 

37.  Punch  a  hole  in  each  end  of  a  small  card,  such  as  a  visiting  card, 
and  in  each  hole  tie  a  piece  of  twine.     Draw  a  cage  on  one  side  of  the  card 
and  an  animal  exactly  opposite  on  the  other.     Revolve  the  card  by  means 
of  the  twine  and  explain  the  effect  produced. 

38.  How  many  distinct  and  consecutive  objects  can  one  see  in  a 
second? 


CHAPTER  XXIII 
COLOR 

134.  Composition  of  Light. — Light,  as  it  ordinarily  comes  to 
us  from  the  sun,  is  called  white  light,  but  if  a  beam  of  this  light 
be  directed  through  a  glass  prism,  we  discover  that,  instead 
of  white  light,  we  have  a  band  of  several  different  colors  called 
the  primary  or  prismatic  colors,  with  red  at  one  end,  violet  at 
the  other,  and  orange,  yellow,  green,  blue,  and  indigo  between. 


"FiG.  58. — Formation  of  the  spectrum  by  a  prism.     (Tower,  Smith 
and  Turton.) 

The  colors  are  due  to  differences  in  the  speed  with  which  the 
rays  of  light  vibrate  and  the  resultant  effects  of  these  rays  on 
the  eye.  Those  which  give  us  the  sensation  of  red,  vibrate 
392,000,000,000,000  times  a  second,  while  the  violet  rays 
vibrate  more  than  twice  as  fast.  Passing  light  through  a  prism 
merely  serves  to  sort  out  the  different  rays.  If  these  are 
brought  to  a  focus  by  a  lens,  or  are  mixed  in  any  other  way, 

160 


COLOR  161 

we  get  white  light  again.  The  rainbow  is  a  natural  spectrum 
into  which  light  is  broken  up  by  falling  raindrops.  Small 
rainbows  may  often  be  seen  in  the  spray  from  waterfalls, 
lawn  sprinklers,  and  the  like.  The  misty  halos  sometimes 
noticed  encircling  the  moon  and  regarded  as  the  forerunners 
of  stormy  weather  are  due  to  similar  causes.  Other  examples 
of  refracted  sunlight  are  the  brilliant  colors  of  the  sky  at  sun- 
rise and  sunset.  The  composition  of  light  may  be  studied 
by  means  of  the  spectroscope.  This  consists  essentially 'of  a 


FIG.  59. — The  spectroscope.     (Tower,  Smith  and  Turton.) 

prism  with  means  for  magnifying  and  measuring  the  rays  of 
light  passing  through  it.  All  luminous  bodies  give  out  char- 
acteristic rays.  When  a  gas  is  heated  enough  to  glow,  it 
produces  a  set  of  colored  lines  in  the  spectroscope,  which  are 
known  as  its  spectrum.  By  means  of  the  spectroscope,  the 
light  from  distant  stars  has  been  examined  and  the  elements 
composing  them  identified.  Only  a  few  of  the  vibrations  com- 
ing to  us  in  sunlight  are  perceptible  to  the  eye.  Beyond  the 
red  end  of  the  solar  spectrum,  as  it  is  called,  are  still  slower 
11 


162  EXPERIMENTAL   GENERAL   SCIENCE 

infra-red  rays  which  the  eye  fails  utterly  to  note,  but  which 
when  properly  handled,  will  affect  the  photographic  plate. 
In  this  region  of  the  spectrum  the  majority  of  the  heat  rays 
also  occur.  Beyond  the  violet  end  of  the  spectrum  are  the 
ultra-violet  rays.  Some  of  these  vibrate  1,500,000,000,000,000 
times  a  second.  These  rays  kill  germs,  cause  skin  to  tan  and 
freckle,  and  may  even  be  used  for  making  photographs, 
though  most  of  the  rays  which  make  ordinary  photographs 
are  found  in  the  violet  end  of  the  spectrum.  Fine  particles 
of  dust,  water,  or  ice  may  act  like  a  prism  in  breaking  up  light 
into  these  primary  colors,  or  they  may  even  stop  some  of  the 
colors  and  allow  the  others  to  come  to  us.  To  such  causes  many 
colors  of  the  sky  and  clouds  are  due. 

135.  Absorption  and  Reflection. — Colored  bodies  have  no 
colors  of  their  own.     We  call  them  colored  only  when  they 
have  the  power  to  reflect  or  absorb  some  of  the  light  rays 
falling  upon  them.     A  piece  of  red  glass  for  instance  is  red 
because  it  absorbs  or  stops  all  the  rays  of  light  except  those 
we  call  red,  allowing  the  latter  to  pass.     A  red  apple,  however, 
is  red  for  a  different  reason.     In  this  case,  it  sorts  out  and 
reflects  red  rays  and  absorbs  all  the  others.     When  a  body 
absorbs  all  the  light  rays,  it  will  of  course  give  back  none,  and 
we  call  it  black.     If  an  apple  be  placed  in  light  which  has  no 
red  rays  in  it,  there  will  be  none  to  reflect,  and  it  will  conse- 
quently appear  black.     Placing  a  green  object  in  red  light 
would  have  the  same  effect.     The  energy  of  the  colors  absorbed 
is  changed  to  heat  which  gives  reason  for  the  statement  that 
black  clothing  is  warmer  than  white.     Red,  being  nearer  the 
warm  end  of  the  spectrum,  is  properly  called  a  warm  color, 
while  blue  and  violet  are  known  as  cold  colors.     White,  as 
we  have  seen,  is  a  mixture  of  all  the  colors. 

136.  Fluorescence. — Some  bodies  have  the  power  to  change 
the  color  of  the  light  falling  upon  them  and  are  said  to  be 
fluorescent.     In  fluorescence,  as  in  phosphorescence,  the  rays 


COLOR  163 

given  out  are  always  slower  than  those  taken  in.  A  solution 
of  chlorophyll,  the  green  coloring  matter  of  plants,  is  green  by 
transmitted  light,  but  the  light  reflected  from  it  has  a  reddish 
hue.  Kerosene  is  also  strongly  fluorescent.  The  greenish 
color  often  reflected  from  the  eyes  of  animals  at  night  is  prob- 
ably also  due  to  fluorescence.  The  X-rays,  or  Roentgen  rays, 
used  for  locating  broken  bones,  bullets,  and  the  like  in  the 
human  body,  are  not  visible  to  the  eye,  but  owing  to  the  fact 
that  they  excite  fluorescence  in  various  substances,  we  are 
able  to  construct  a  fluoroscope  by  means  of  which  the  shadows 
of  the  bones  and  other  dense  objects  may  be  studied. 

137.  Complementary  Colors. — Not  only  may  white  light 
be  broken  up  into  the  seven  primary  colors,  but  we  can  pro- 
duce white  light  by  a  proper  mixture  of  these  colors.  If  any 
of  the  seven  colors  be  missing,  however,  the  light  will  not  be 
white.  Since  any  of  the  primary  colors  may  be  produced  by 
the  proper  mixture  of  red,  green  and  violet-blue,  these  latter 
are  often  regarded  as  the  real  primary  colors.  The  color  which 
must  be  added  to  another  color  to  make  white  light  is  called 
its  complementary  color.  Among  sets  of  complementary  colors 
are  red  and  blue-green,  yellow  and  blue-indigo,  greenish-yellow 
and  violet,  and  orange  and  light  blue.  A  colored  object  is 
always  made  more  conspicuous  by  being  near  its  comple- 
mentary color.  It  is  to  be  noted  that  when  pigments  are 
mixed,  they  do  not  always  give  results  in  accordance  with  the 
statement  just  made,  for  the  reason  that  pigments  are  not 
colors  but  substances  which  reflect  colors.  Yellow  and  blue 
rays  give  white  light,  but  yellow  and  blue  pigments  give 
green  color.  Colors  differ  considerably  in  their  carrying  power, 
and  this  does  not  depend  entirely  upon  their  wave  length. 
Yellow  is  visible  from  the  greatest  distance.  As  the  twilight 
deepens,  blue  flowers  are  the  first  to  become  indistinguishable, 
then  follow  the  red  and  pink,  but  the  yellow  are  usually 
visible  except  on  the  darkest  nights. 


164  EXPERIMENTAL   GENERAL    SCIENCE 

138.  The  Eye  and  Color. — Color,  as  we  have  seen,  is  really 
a  sensation  set  up  in  the  retina  by  light  of  a  certain  wave 
length  and  from  the  retina  transmitted  to  the  brain.  There 
seem  to  be  three  sets  of  these  nerve  endings  sensitive  to  red, 
green  and  blue  respectively.  When  any  of  these  are  defective 
or  refuse  to  carry  their  proper  sensations,  the  eye  will  be  color- 
blind. A  person  color-blind  for  red  will  have  difficulty  in 
distinguishing  a  red  apple  from  the  green  leaves  by  color  alone. 
Yellow  and  blue  are  the  colors  most  easily  distinguished  by 
the  color-blind.  The  nerves  which  carry  color  sensations  are 
easily  tired  and,  if  overtaxed,  may  fail  to  report  accurately  for 
a  time.  When  one  looks  intently  at  a  red  object  for  a  few 
seconds  and  then  at  a  white  wall  or  curtain,  he  will  see  the 
image  of  the  object  in  green,  since  the  tired  nerves  do  not  now 
respond  to  that  color  in  ordinary  light  and  only  the  comple- 
mentary colors  are  reported  to  the  brain. 

Practical  Exercises 

1.  How  many  times  is  a  beam  of  light  turned  in  passing  through  a 
prism  ? 

2.  Why  do  openings  into  dark  places  such  as  cellars,  always  appear 
black? 


3.  Why  does  the  pupil  of  the  eye  appear  black? 

4.  Why  is  the  interior  of  a  camera  always  painted  black  ? 

5.  Put  a  strong  solution  of  soap  and  water  in  a  flask  and  look  through 
it  toward  the  light.     What  is  its  general  color? 

6.  Look  at  the   flask  by  reflected  light.     What  is  the  general  color? 

7.  How  did   the   particles   of  soap  in  the  water  produce  the  effects 
noted  in  the  foregoing  experiments? 


COLOR  165 

8.  Look  at  the  sun  through  a  piece  of  smoked  glass,  and  explain  the 
change  in  color  noted. 

9.  What  causes  the  sun  to  have  a  red  hue'at  sunset? 

10.  Why  does  the  sky  appear  blue? 

11.  What  color  would  the  sky  be  if  there  were  no  dust  in  the  air? 

12.  Why  do  distant  hills  always  look  blue? 

13.  What  effect  does  the  absence  of  dust  have  on  twilight? 

14.  When  are  the  colors  of  sunset  brightest,  on  a  clear  or  on  a  partly 
cloudy  day?     Why? 

15.  What  rays  of  light  do  plants  absorb? 


16.  Look  at  a  blue  object  through  a  red  glass.     Explain  the  change 
in  color. 


17.  What  color  would  a  red  object  appear  in  blue  light?     Why? 

18.  Look  at  a  white  object  through  three  combined  sheets  of  glass, 
red,  green,  and  blue  respectively.     Explain  the  result. 

19.  The  mercury-vapor  lamp,  much  used  in  factories,  photograph 
studios,  and  the  like,  give  a  bluish-green  light  with  few  or  no  red  rays. 
What  would  be  the  effect  of  putting  a  red  glass  chimney  over  the  light? 

20.  Why  do  people  look  pale  in  blue  light? 

21.  Why  is  it  difficult  to  match  colors  by  artificial  light? 


166  EXPERIMENTAL    GENERAL   SCIENCE 

22.  Why  is  bluing  added  to  water  in  which  clothes  are  rinsed  in 
laundering? 


23.  What  color  of  paper  is  best  for  wrapping  up  white  goods  to  give 
them  a  white  appearance? 

24.  Should  a  girl  with  red  hair  wear  blue?     Why? 

25.  Hold  a  piece  of  green  glass  before  one  eye,  and  a  piece  of  red  glass 
before  the  other,  and  look  at  some  white  object  for  a  few  minutes.     Then 
look  through  one  of  the  glasses,  first  with  one  eye  and  then  the  other. 
Explain  the  difference  in  the  brightness  of  the  color  noted. 

26.  Cut  various  shapes  out  of  black  paper.     Lay  them  on  a  green  or 
red  surface,  such  as  a  book  cover,  and  cover  them  with  a  thin  sheet  of 
white  tissue  paper.     Hold  in  the  light  and  explain  the  apparent  color 
of  the  objects. 


27.  Why  does  the  photographer  find  it  necessary  to  use  a  red  or  orange 
light  in  his  dark  room? 


28.  Examine  plants  grown  in  the  dark,  or  the  grass  over  which  a  board 
has  lain  for  a  few  days.     What  effect  has  light  on  the  color  of  plants? 

29.  Why  does  a  blue  dress  look  black  in  red  light? 

30.  In  photographing  colored  objects,  a  color-screen  of  light  yellow 
glass  is  often  used.     How  does  this  assist  the  reds  and  yellows  to  register 
properly? 


CHAPTER  XXIV 
SOUND 

139.  Vibrations  in  Air. — Sound,  like  light,  consists  of  vibra- 
tions which  excite  certain  of  our  nerve  endings  and  cause  char- 
acteristic sensations  to  be  transmitted  to  the  brain.  In  one 
case,  the  vibrations  fall  on  the  retina  producing  light,  vision, 
and  color;  in  the  other,  they  fall  on  the  ear  and  cause  sensa- 
tions of  hearing.  Sound  differs  from  light  in  consisting  of 
waves  in  ordinary  matter  instead  of  in  the  ether,  and  in  con- 
sequence they  move  much  more  slowly  and  cannot  cross  a 


FIG.  60. — Recording  the  vibrations  of  a  tuning  fork. 

vacuum.  The  speed  of  sound  is  also  affected  by  the  medium 
in  which  it  travels.  In  ordinary  air,  it  moves  about  1100  feet 
a  second,  in  water  nearly  five  times  as  fast,  and  in  iron  or  steel 
fifteen  times  as  fast.  Even  this  latter  speed  is  in  marked  con- 
trast to  the  speed  of  light,  which  is  nearly  186,000  miles  a 
second  under  all  circumstances.  In  general,  the  denser  the 
substance,  the  more  rapidly  sound  travels  in  it,  though  this 
statement  is  subject  to  some  modifications  since  the  elasticity 
of  the  substance  in  which  it  moves  must  also  be  taken  into 

167 


168  EXPERIMENTAL    GENERAL    SCIENCE 

account.  Sound  moves  most  rapidly  in  elastic  bodies.  Since 
adding  moisture  to  the  air  increases  its  elasticity,  we  commonly 
hear  distant  sounds  more  distinctly  just  before  a  storm. 
Sound  waves  may  be  thought  of  as  a  series  of  alternating  com- 
pressions and  rarifications  in  the  mediums  through  which  they 
pass.  They  tend  to  spread  out  in  all  directions  from  their 
source  and  thus,  coming  constantly  into  contact  with  a  greater 
number  of  molecules  which  must  be  caused  to  vibrate,  they 
gradually  lose  their  energy  and  diminish  in  intensity.  When 
sound  waves  are  kept  from  spreading,  as  in  the  speaking-tube 
or  megaphone,  they  carry  much  farther.  The  reason  one  can 
usually  hear  sounds  so  distinctly  across  the  water  is  because 
the  layers  of  denser  air  above  the  water  prevent  the  sound 
from  rising. 

140.  Echoes. — Sound,  like  light,  may  be 
turned  or  reflected,  and  can  also  be  brought 
to  a  focus.     When  reflected,  the  angle  of  in- 
—-,  cidence     equals    the    angle    of    reflection. 

4LJ  When  a  reflected  sound  reaches  our  ears  after 

vr      the  original  sound  has  ceased,  we  call  it  an 


FIG.     61.—  Tun-  echo  but  if  it  reaches  us  in  a  shorter  period  of 
01(Z>wjnat~  time>  ^  usually  serves  merely  to  strengthen 
the  original  sound.     Since  the  sensation  of 


sound  persists  about  Ho  second,  the  reflecting  surface  must  be 
at  least  56  feet  away  to  cause  an  echo.  If  nearer,  the  sound 
waves  would  have  time  to  go  and  return  before  the  original 
sound  ceased.  Echoes,  however,  may  be  produced  from  sur- 
faces much  nearer  the  observer,  but,  in  such  cases,  the  waves 
are  reflected  from  one  surface  to  another  just  as  light  may  be 
reflected  from  one  mirror  to  another.  The  usual  reflecting  sur- 
face is  a  wall,  wood,  or  cliff,  but,  on  occasion,  clouds  or  layers  of 
air  of  different  density  may  serve  as  reflecting  surfaces  also.  A 
sounding-board  is  often  placed  back  of  the  speaker's  platform 
in  large  rooms  to  reinforce  the  tones  of  the  speaker.  When 


SOUND 


169 


no  reflecting  surfaces  are  near,  it  is  much  more  difficult  to 
hear  the  speaker.  This  explains  the  difficulty  one  has  in 
understanding  a  speaker  in  the  open  air.  When  sound  is 
reflected  from  several  surfaces  at  different  distances,  a  suc- 
cession of  echoes  following  close  upon  one  another  may  be  pro- 
duced. These  we  call  reverberations.  The  roll  of  thunder  is 
thus  produced  by  the  reflection  of  the  original  sound  from 
different  clouds. 

141.  Sympathetic  Vibrations. — The  time  required  for  one 
vibration  of  a  body  is  called  its  period.     If  a  vibrating  body  be 
brought  near  another  with  the  same  period, 

the  latter  will  soon  begin  to  vibrate  in  har- 
mony with  it.  Vibrations  of  this  kind  are 
called  sympathetic  vibrations.  Other  bodies 
may  be  forced  to  vibrate  out  of  their  natural 
period  when  brought  into  contact  with  a 
vibrating  body.  Thus  the  body  of  a  violin 
vibrates  in  harmony  with  the  strings  stretched 
across  it.  Since  the  volume  of  sound  given 
out  by  the  vibrating  body  is  proportional  to 
the  surface  vibrating,  forced  vibrations  of  this 
kind  largely  increase  the  original  sound.  F.I<\6L~rA  Tnt 

e  venient   method   of 

The  property  of  a  body  which  enables  it  to  changing  the  length 
vibrate  in  harmony  with  another  is  called  of.  a  vibrating  air 

*  column. 

resonance. 

142.  Distinguishing    Sounds. — When    a    musical    note    is 
sounded,  there  is  produced,  in  addition  to  the  fundamental 
tone,  a  variety  of  others,  known  as  overtones,  that  give  char- 
acter to  the  different  musical  sounds  and  enable  us  to  distin- 
guish the  notes  of  different  instruments  in  an  orchestra,  to 
recognize  the  voices  of  our  friends  over  the  telephone,  and  the 
like.     Should  these  overtones  be  suppressed,  the  ear  would 
be  unable  to  distinguish  the  notes  produced  by  the  piano  or 
flute  from  those  of  the  human  voice. 


170  EXPERIMENTAL   GENERAL   SCIENCE 

Practical  Exercises 

1.  How  does  clapping  the  hands  or  firing  a  cannon  produce  sound? 

2.  Recall  the  playing  of  a  band  at  a  distance.     Do  different  sounds 
have  different  rates  of  speed,  or  do  they  travel  with  the  same  speed  in  the 
same  medium? 


3.  How  far  away  is  the  lightning  if  the  thunder  is  heard  three  seconds 
after  the  flash  is  seen? 


4.  A  steamer  five  miles  from  shore  is  seen  to  blow  her  whistle.     How 
long  before  the  sound  would  be  heard  by  a  person  on  shore? 

6.  Whore  would  you  expect  conversation  to  be  more  easily  heard, 
in  deep  mines  or  on  mountain  tops?     Why? 


6.  How  far  away  is  the  reflecting  surface  if  an  echo  is  heard  half  a 
second  after  the  original  sound? 


7.  How  long  will  it  take  for  an  echo  to  reach  you  if  the  reflecting 
surface  is  1100  feet  away? 


8.  Could  one  hear  better  by  placing  the  small  end  of  a  megaphone 
to  the  ear?     Why? 


9.  Why  are  echoes  more  likely  to  occur  in  a  large  than  in  a  small 
room? 


10.  Why  do  empty  rooms  often  produce  echoes  when  the  same  rooms 
furnished  do  not? 


11.  When  a  sea-shell  is  held  to  the  ear,  a  roaring  sound,  which  some 
people  believe  to  be  the  roaring  of  the  sea,  can  be  heard.  What  causes 
the  sound? 


SOUND  171 

12.  When  a  comb  is  drawn  rapidly  across  the  edge  of  a  card,  would 
you  consider  the  sound  produced  a  musical  sound  or  only  noise? 

13.  Suppose  the  card  held  on  the  rim  of  a  rapidly  revolving  and  regu- 
larly notched  wheel.     Would  you  call  the  sound  music  or  noise? 

14.  Why  do  the  wings  of  a  bee  make  a  musical  note  when  the  wings 
of  a  bird  in  flight  do  not? 

15.  Of  what  use  is  the  reed  or  thin  flap  of  metal  in  a  harmonica  or 
mouth  organ? 

16.  How  does  placing  the  Jew's-harp  in  front  of  the  mouth  make  it 
sound  louder? 

17.  Stretch  a  string  across  two  supports  in  such  a  way  that  it  is  free 
to  vibrate.     When  does  it  give  out  the  higher  note,  when  it  is  loosely  or 
tightly  stretched? 

18.  When  does  it  vibrate  most  rapidly? 

19.  Using  the  finger  for  a  support,  cause  different  lengths  of  the  string 
to  vibrate.     Which  gives  off  the  higher  note,  a  short  or  a  long  string? 

20.  Is  the  foregoing  true  of  pianos,  harps,  and  violins? 

21.  Explain  the  humming  of  telegraph  and  telephone  wires. 

22.  What  produces  the  sounds  in  an  aeolian  harp? 

23.  Which  would  you  expect  to  give  the  higher  note,  a  large  or  a  small 
tuning  fork? 

24.  Suppose  the  wheel  mentioned  in  question  13  to  have  its  speed 
suddenly  increased.    What  effect  would  this  have  on  the  tone  produced? 


172  EXPERIMENTAL   GENERAL   SCIENCE 

26.  Strike  a  tuning  fork  and  immediately  hold  the  base  of  the  fork  on 
the  top  of  a  wooden  table  or  a  wooden  box.     Explain  the  sound  produced. 

26.  Strike  the  fork  again  and  hold  it  over  the  mouth  of  a  tall  cylinder. 
Pour  water  into  the  cylinder,  a  little  at  a  time,  until  you  get  a  clear  note 
from  the  cylinder.     How  does  the  column  of  air  in  the  cylinder,  vibrating 
in  sympathy  with  the  fork,  affect  the  original  sound? 

27.  Try  a  tuning  fork  of  a  different  size.     Does  the  air  column  vibrate 
with  any  sound  or  only  those  with  which  it  is  in  sympathy? 

28.  Using  the  loud  pedal  of  the  piano,  sound  a  full  note  with  the  voice 
and  account  for  the  response  from  the  piano. 

29.  Why  do  the  windows  of  a  church  sometimes  rattle  when  a  particu- 
larly deep  note  is  played  on  the  organ? 

30.  Draw  a  small  glass  tube  out  to  a  slender  point,  attach  it  to  a  gas 
jet  by  a  rubber  tube,  fix  in  an  upright  position,  and  light  the  gas.     Now 
slowly  pass  a  longer  and  larger  tube  over  the  flame.     Account  for  the 
sound  produced. 

31.  What  gives  resonance  to  the  flute  or  fife? 

32.  What  gives  resonance  to  the  drum? 

33.  What  part  of  the  respiratory  tract  gives  resonance  to  the  human 
voice? 

34.  How  many  notes  in  the  musical  scale? 

35.  Is  there  a  single  scale  or  will  any  other  series  of  tones  with  the 
same  difference  in  vibration  produce  a  scale? 

36.  In  the  xylophone,  a  scale  is  produced  by  pieces  of  wood  of  different 
lengths.     Explain. 


CHAPTER  XXV 
FORCE  AND  MOVING  BODIES 

143.  Momentum  and  Inertia. — When  a  body  is  at  rest,  it 
cannot  be  moved  without  applying  some  external  force  to  it; 
that  is,  energy  must  act  upon  it  in  order  to  move  it.  When 
it  is  once  set  in  motion,  however,  it  offers  a  similar  resistance 
to  any  effort  to  stop  it.  The  resistance  which  a  body  thus 
offers  to  any  attempt  to  change  its  condition  is  called  its 
inertia.  If  a  moving  body  meets  with  no  opposition,  it  will  go 
on  in  a  straight  line  forever.  On  the  earth,  however,  bodies 
ultimately  meet  with  enough  resistance  in  Drubbing  against 
the  air  or  other  forms  of  matter  to  bring  their  motion  to  an 
end.  When  a  body^  is  in  motion,  the  resistance  which  it 
offers  to  being  stopped  is  spoken  of  as  its  momentum.  Momen- 
tum is  not  the  same  as  speed,  however,  for  a  heavy  body,  such 
as  a  cannon-ball,  moving  slowly  may  offer  more  resistance  to 
being  stopped  than  a  lighter  body  moving  with  a  much  higher 
speed.  If  a  second  force  be  applied  to  a  moving  body,  its 
effects  depend  upon  the  direction  from  which  it  is  applied. 
If  applied  in  the  direction  in  which  the  body  is  moving,  it 
increases  its  speed;  if  applied  in  the  opposite  direction,  it  re- 
duces the  speed,  or,  if  large  enough,  may  either  stop  it  entirely 
or  cause  it  to  move  in  the  opposite  direction.  If  applied  in 
any  other  direction,  the  body  will  take  a  new  course  which  is 
the  exact  average  of  the  two  courses  which  it  would  have  fol- 
lowed had  each  force  acted  separately  upon  it.  We  have  an 
illustration  of  this  when  any  heavy  object  is  tied  to  a  string 
and  swung  around  in  a  circle.  The  moving  body  tends  to  fly 
away  in  a  straight  line,  but  being  constantly  pulled  out  of  its 

173 


174  EXPERIMENTAL   GENERAL   SCIENCE 

course  by  the  string,  it  takes  a  circular  path.  When  a  wheel 
or  other  object  is  rotating,  there  is  always  present  this  tendency 
for  each  particle  to  fly  off  into  space.  The  particular  force 
which  causes  this  is  called  the  centrifugal  force.  Any  force 
which  tends  to  pull  the  particles  of  a  moving  body  toward  the 
center  of  a  circle  is  called  the  centripetal  force.  In  all  cases 
where  a  force  acts,  there  is  a  reaction  equal  to  the  action. 
A  moving  body  may  be  stopped  only  when  the  resistance  to 
its  progress  is  equal  to  its  momentum.  If  the  resistance  is 
^greater  than  the  momentum,  as  when  we  strike  a  moving  ball 
with  a  bat  moving  in  the  opposite  direction,  a  new  motion 
may  be  set  up  which  is  due  to  the  excess  momentum  from  the 
bat  which  is  now  imparted  to  the  ball. 

144.  Friction. — The  resistance  which  moving  bodies  meet 
in  rubbing  past  other  bodies  is  called  friction.  This  resist- 
ance is  due  to  th§  fact  that  surfaces  which  appear  smooth  are 
never  entirely  so.  Even  polished  surfaces,  such  as  glass  and 
metal,  appear  minutely  roughened  when  viewed  with  a  micro- 
scope. When  two  surfaces  are  in  contact,  their  irregularities 
fit  into  one  another  and  thus  develop  resistance  to  the  passage 
of  the  one  over  the  other.  In  practice,  it  has  been  found  that 
a  given  body  will  often  move  over  a  body  of  an  entirely 
different  substance  more  readily  than  over  another  body  like 
itself.  This  is  because  different  substances  may  have  differ- 
ent irregularities  in  them  and  therefore  fail  to  completely 
interlock.  For  this  reason,  the  journals  in  which  steel  shafts 
turn  are  often  made  of  brass  or  babbitt  metal.  Owing  to  the 
nature  of  the  motion,  rolling  friction,  as  when  a  ball  or  wheel 
rolls  on  a  surface,  develops  less  resistance  than  sliding  friction 
in  which  one  surface  simply  slides  over  another.  The  effort 
needed  to  overcome  friction  at  starting  is  much  greater  than 
is  required  to  keep  the  body  moving  after  once  started.  In 
either  case,  however,  the  friction  is  proportional  to  the  pres- 
sure; the  heavier  the  body  to  be  moved,  the  greater  the  effort 


FORCE   AND    MOVING  BODIES  175 

needed  to  move  it.  Oil,  grease,  and  graphite  fill  up  the  irregu- 
larities of  surfaces  in  contact  and  thus  reduce  friction.  The 
area  of  the  surfaces  in  contact  does  not  usually  affect  friction, 
nor  does  an  increase  in  speed  when  a  solid  is  moving  over 
another  solid,  but  when  the  solid  is  moving  in  water  or  air, 
friction  increases  with  speed.  It  requires  proportionately 
more  energy  to  drive  a  train  or  steamship  at  high  speed  than 
it  does  to  run  them  at  a  more  moderate  velocity. 

145.  Advantages  of  Friction. — Friction  has  its  advantages 
as  well  as  its  disadvantages.     Were  it  not  for  friction,  nails 
would  not  hold,  belts  would  slip  over  pulleys  without  turning 
them,   and  walking  would  be  impossible.     We  realize  the 
truth  of  the  latter  statement  when  we  attempt  to  walk  on 
smooth  ice  or  a  highly  polished  floor.     Sawing,  filing,  polish- 
ing, and  similar  operations  could  not  proceed  without  friction. 
The  sand-blast  for  cutting  designs  on  glass  and  the  like,  also 
owes  its  efficiency  to  friction. 

146.  Gravity. — An  important  force  tending  to   move  all 
bodies  is   called   gravity.     This  is   a    mysterious    attraction 
existing  throughout  the  universe  which  tends  to  draw  all 
bodies  toward  one  another.     The  pull  of  gravity  is  exactly 
proportional  to  the  mass  of  the  body.     A  heavy  body  therefore 
exerts  a  stronger  pull  than  a  lighter  one,  but  it  exerts  no  more 
pull  in  proportion  to  its  mass.     Gravity  also  acts  as  if  the 
entire  mass  of  the  body  were  at  the  center  of  its  mass.     It 
decreases  rapidly  as  the  distance  between  these  centers  in- 
creases, but  notwithstanding  this,  it  is  gravity  that  keeps  the 
stars,  suns,  and  planets  in  their  proper  paths.     The  same  force 
acting  between  the  sun,  moon,  and  earth,  is  the  cause  of  the 
tides.     It  is  also  the  attraction  of  the  earth  for  all  bodies  upon 
it  that  gives  them  weight.     When  we  lift  anything,  we  exert 
sufficient  force  to  overcome  the  pull  of  the  earth  upon   it. 
When  gravity  is  the  only  force  acting  on  a  falling  body,  its 
path  is  a  straight  line  toward  the  center  of  the  earth.     Masons, 


176  EXPERIMENTAL   GENERAL   SCIENCE 

carpenters,  and  other  artisans  make  use  of  this  force  by 
means  of  the  plumb-bob,  a  top-shaped  piece  of  metal  sus- 
pended by  a  string.  The  string  always  takes  a  position 
perpendicular  to  the  earth's  surface,  and  a  line  at  right 
angles  to  this  is  horizontal. 

147.  Equilibrium. — Since  the  attraction  of  gravity  always 
acts  toward  the  center  of  its  mass,  the  center  of  gravity  in  a 
body  is  that  point  upon  which  it  will  exactly  balance  itself. 
When  this  center  is  near  the  base  of  the  body,  as  in  a  book 
lying  on  its  side,  it  resists  any  attempt  to  change  its  position 
or  upset  it.  It  is  therefore  said  to  be  in  stable  equilibrium. 
If,  however,  the  center  of  gravity  is  so  located  that  moving 
the  body  will  lower  the  center  of  gravity,  the  body  is  in  an 
unstable  equilibrium  and  easily  upset.  A  meter  stick  standing 
on  end  is  in  unstable  equilibrium.  In  a  few  bodies,  a  ball  for 
instance,  the  center  of  gravity  is  so  placed  that  moving  them 
neither  raises  nor  lowers  it.  Such  bodies  are  said  to  be  in 
neutral  equilibrium. 

Practical  Exercises 

1.  Why  cannot  one  fire  a  rifle  around  a  tree? 


2.  Why   can   one   jump  farther  with  a  running  start  than  he  can 
without? 


3.  Why  does  a  heavy  flywheel  cause  machines  to  run  more  smoothly? 

4.  Why  may  one  escape  a  close  pursuer  by  dodging? 

5.  How  does  beating  a  carpet  get  the  dust  out  of  it? 


6.  When  a  car  suddenly  goes  around  a  curve  in  which  direction  are 
the  passengers  thrown,  toward  or  away  from  the  center  of  the  curve? 
Why? 


FORCE  AND  MOVING  BODIES          177 

7.  When  a  car  in  which  we  are  riding  stops  suddenly,  we  are  thrown 
forward.     Why? 


8.  In  what  direction  are  we  thrown  when  a  car  starts  suddenly  ?    Why  ? 


9.  In  carrying  a  glass  full  of  water,  why  is  it  likely  to  spill  if  we  stop 
suddenly? 


10.  Lay  a  small  card  over  the  mouth  of  a  drinking  glass  and  put  a  coin 
on  the  card.  Drive  the  card  away  horizontally  by  a  smart  snap  of  the 
finger  and  explain  the  action  of  the  coin. 


11.  Place  a  penny  on  a  cloth-covered  table  and  invert  over  it  a  drink- 
ing glass  propped  up  by  three  larger  coins.     By  scratching  on  the  cloth 
near  the  penny,  it  may  be  made  to  creep  out  from  under  the  glass. 
Explain. 

12.  Why  is  one  likely  to  be  thrown  down  when  jumping  from  a  rapidly 
moving  vehicle? 


13.  Why,  in  jumping  from  a  small  boat,  does  the  boat  move  away  as 
we  jump? 


14.  How  is  it  possible  to  drive  a  nail  by  striking  it  with  a  hammer? 


15.  When  one  cracks  an  egg  by  striking  it  against  a  hard  object,  is  it 
action  or  reaction  that  breaks  the  shell? 


16.  Mud  which  will  stick  to  a  slowly  revolving  wheel  will  be  thrown 
off  when  the  wheel  moves  faster.     Why? 


17.  Grindstones,  emery  wheels,  and  the  like  are  sometimes  turned  so 
fast  that  they  break.     Why? 

12 


178  EXPERIMENTAL   GENERAL   SCIENCE 

18.  Why  can  one  whirl  a  bucket  of  water  in  a  perpendicular  circle 
without  spilling  it? 


19.  In  large  laundries,  the  clothes  are  often  dried  by  being  placed  in 
a  cylinder  having  many  openings  and  revolved  rapidly.     How  does  this 
dry  the  clothes? 

20.  The  cream  separator  used  in  dairies  is  essentially  a  rapidly  revolv- 
ing bowl  into  which  the  milk  is  run.     Do  you  infer  that  the  cream  goes 
to  the  center  or  to  the  outer  part  of  the  bowl.     Why? 

21.  Where  does  a  stream  run  faster,  near  the  banks  or  in  midstream? 
Why? 

22.  Would  an  increase  in  the  friction  between  the  wheels  of  a  loco- 
motive and  the  rails  be  advantageous  or  not?    Why? 

23.  Explain  the  use  of  sand  on  the  rails  when  the  track  is  slippery. 

24.  A  sheet  of  paper  flutters  to  the  ground  but  the  same  paper  made 
into  a  ball  falls  more  rapidly.     Why? 


25.  Why  will  a  coin  fall  to  the  ground  more  quickly  than  a  feather? 

26.  Why  do  ball  bearings  make  machines  run  more  easily? 


27.  Why  are  the  shafts  of  fine  watches  set  in  bearings  made  of  precious 
stones? 


28.  On  which  would  a  marble  roll  farther,  a  bare  floor  or  one  covered 
with  carpet?    Why? 

29.  Why  is  it  more  difficult  to  walk  against  a  stiff  breeze  than  against 
a  light  one? 


FORCE  AND  MOVING  BODIES          179 

30.  How  does  applying  brakes  to  the  wheels  of  a  train  reduce  its 
speed? 

31.  What  force  do  we  overcome  when  we  drive  a  nail? 


32.  The  earth  travels  around  the  sun  in  a  nearly  circular  path.  Can 
you  explain  why  the  attraction  of  gravity  does  not  cause  it  to  fall  into 
the  sun? 


33.  Recalling  the  shape  of  the  earth,  decide  whether  a  piece  of  gold 
weighing  exactly  an  ounce  at  the  north  pole  would  weigh  more  or  less 
if  carried  to  the  equator? 

34.  Where  would  a  body  weigh  more,  at  sea-level  or  on  a  mountain 
top?     Why? 


35.  The  planet  Jupiter  is  much  larger  than  the  earth.  If  it  has  the 
same  density  as  the  earth,  would  a  man  weigh  more  or  less  if  transported 
to  Jupiter?  Why? 


36.  Suppose  the  earth  to  rotate  twice  as  fast  as  it  does  at  present. 
What  effect  would  this  have  on  the  weight  of  objects?     Why? 


37.  Name  the  kinds  of  equilibrium  represented  by  the  following:  a 
ball  on  a  sloping  surface,  a  moving  pendulum,  a  cone  resting  on  its  side, 
a  cone  resting  on  its  base,  a  spinning  top,  a  cube  of  wood,  an  egg,  walking 
a  rope,  a  man  standing. 

38.  When  one  stands  erect,  is  the  center  of  gravity  above  or  below  the 
point  of  support? 

39.  Why  is  it  so  difficult  to  stand  up  in  a  small  boat? 

40.  Why  do  we  lean  forward  when  getting  up  from  a  chair? 


180  EXPERIMENTAL   GENERAL   SCIENCE 

41.  When  one  is  carrying  a  bucket  of  water  or  other  heavy  object  in 
one  hand,  why  is  the  other  held  away  from  the  body? 

42.  Why  do  we  lean  forward  when  walking  up  hill? 

43.  Why  do  we  swing  our  arms  when  we  walk? 

44.  Stand  with  your  back  to  the  wall  and  without  moving  the  feet, 
try  to  pick  up  an  object  placed  at  the  toe  of  your  shoe.     Explain  your 
failure. 

45.  Explain  how  "walking  is  a  perpetual  falling." 

46.  What  causes  the  great  pressure  at  the  bottom  of  the  ocean? 


CHAPTER  XXVI 


LONGITUDE  AND  TIME 

148.  Locating  Points  on  a  Globe. — It  would  be  very  diffi- 
cult to  indicate  a  point  upon  a  stationary  ball  or  globe,  for  it 
has  neither  up  nor  down,  sides  nor  ends,  nor  points  of  the 
compass.  When  such  a  body  is  rotating,  however,  the  task 
becomes  very  easy.  We  have  only  to  call  the  imaginary  line 
about  which  it  spins  its  axis,  and  the  two  points  where  this 
line  comes  to  the  surface,  its  poles,  to  get  two  locations  upon 
it  that  do  not  change.  If  a  set  of 
lines  are  now  imagined  passing 
around  the  globe  through  these 
poles,  and  another  set  extending 
around  it  at  right  angles  to  them, 
any  place  may  readily  be  located 
by  noting  its  distance  from  the 
nearest  line  of  each  set.  The  earth 
is  such  a  globe,  and  the  location  of 
points  upon  it  is  determined  in  this 
manner.  If  one  turns  his  back  to 
the  sun  at  noon  in  our  part  of  the 
world,  he  will  be  facing  that  pole  called  the  north  pole.  The 
direction  on  his  right  will  be  east  and  on  his  left  west.  South 
will  be  behind  him.  The  circles  passing  through  the  poles  are 
known  as  meridians,  and  those  running  at  right  angles  to  these 
are  parallels.  The  distance  of  a  place  from  a  given  meridian 
expressed  in  degrees,  is  called  its  longitude,  and  the  distance 
north  or  south  of  the  great  circle,  called  the  equator,  that  passes 
around  the  earth  midway  between  the  poles  is  its  latitude. 

181 


FIG.  63. — Important  circles  on 
the  earth. 


182  EXPERIMENTAL   GENERAL   SCIENCE 

149.  Distances  on  the  Earth. — Since  the  earth  makes  one 
rotation  on  its  axis  every  24  hours,  we  can  express  distances 
east  and  west  around  the  earth  in  terms  of  either  time,  length, 
or  longitude.     In  north  and  south  directions  we  can  express 
distance  only  in  terms  of  length  or  latitude,  because  it  is  the 
turning  of  the  earth  on  its  axis  that  gives  us  the  measure  of 
time.     The  distance  around  the  earth  at  the  equator  is  about 
25,000  miles,  and  since  every  circle  has  360  degrees  in  it,  the 
length  of  one  degree  on  the  equator  would  be  nearly  72  miles. 
North  and  south  of  the  equator,  however,  the  circles  grow 
successively  smaller  and  the  length  of  a  degree  is  necessarily 
shorter  also,  but  the  same  number  of  degrees  pass  beneath  the 
sun  every  hour,  no  matter  where  located.     The  great  circles, 
or  meridians,  which  pass  north  and  south  through  the  poles, 
are  all  of  the  same  size  and  there  is  not  this  difference  in  the 
length  of  the  degrees  north  and  south.     Knowing  the  length 
of  a  degree  on  a  given  circle,  one  can  readily  determine  the 
distance  in  miles  between  two  places  on  it  by  the  difference 
in  latitude  or  longitude. 

150.  Time  on  the  Earth. — As  the  earth  turns  about  in  the 
sunlight,  one-half  is  always  illuminated  and  one-half  always 
in  shadow,  but  these  are  never  stationary  areas.     Owing  to 
the   earth's   motion,   light  and   darkness  follow  each  other 
around  it  at  the  rate  of  15  degrees  (^24  of  360)  an  hour,  or 
one  degree  every  four  minutes.     To  an  observer  on  the  earth, 
the  sun  appears  to  move  from  east  to  west  at  the  same  rate. 
When  the  sun  is  exactly  overhead  at  a  given  place,  it  is  noon 
at  that  place  as  well  as  at  all  other  places  on  the  same  meridian. 
Fifteen  degrees  east  of  this  meridian,  it  would  be  one  hour 
later,  and  15  degrees  west,  it  would  be  one  hour  earlier.     This 
is  true  noon  by  "sun  time." 

161.  Time  Belts. — In  a  great  many  places,  true  noon  and 
the  noon  registered  by  the  clocks  and  watches  are  not  the 
same,  the  difference  between  them  being  often  nearly  an  hour. 


LONGITUDE   AND    TIME  183 

This  is  because  man  has  agreed  to  a  sort  of  artificial  noon  more 
suitable  to  his  interests.  Since  the  sun  is  steadily  moving 
westward,  true  noon  does  the  same,  and  if  the  sun  time  were 
used,  the  time  at  even  nearby  places  would  not  be  the  same. 
To  facilitate  the  running  of  trains  and  other  work  depending 
upon  exact  time,  the  surface  of  the  earth  has  been  divided 
into  time  belts,  each  15  degrees  wide,  in  which  the  clocks  record 
time  alike.  When  it  is  true  noon  over  the  center  of  such  a 
time  belt,  it  is  assumed  to  be  noon  throughout  the  belt,  though 
in  some  parts  it  is  earlier  and  in  others  later  than  noon. 
There  are  five  of  these  time  belts  in  North  America  which, 
beginning  in  the  east,  are  known  respectively  as  Intercolonial, 
Eastern,  Central,  Mountain  and  Pacific  time.  Time,  according 
to  this  arrangement,  is  known  as  standard  time.  The  meridians 
that  form  the  centers  of  the  time  belts  are  the  60th,  75th,  90th, 
105th,  and  120th  west  of  the  meridian  of  Greenwich.  When 
a  traveller  passes  from  one  time  belt  to  another,  he  sets  his 
watch  forward  or  backward  an  hour,  according  to  the  direc- 
tion in  which  he  is  traveling.  Were  it  not  for  the  time  belts, 
his  watch,  on  comparison  with  local  time,  would  seem  to  be 
constantly  gaining  or  losing  time.  The  old  abbreviations, 
a.m.  for  ante-meridian,  and  p.m.  for  post-meridian,  have  thus 
lost  to  some  extent  their  significance  since  the  adoption  of 
standard  time. 

152.  The  Earth's  Axis  and  the  Zones.— The  earth's  axis 
is  not  at  right  angles  to  a  line  drawn  from  the  sun  to  the  earth, 
but  is  tilted  23^  degrees  from  the  perpendicular.  In  con- 
sequence of  this,  the  north  pole  is  inclined  toward  the  sun 
during  our  summer  season  and  away  from  it  in  winter.  Ex- 
actly half  of  the  earth  is  always  toward  the  sun,  but  because 
of  the  tilted  axis,  the  sunshine  lacks  23^  degrees  of  reaching 
the  south  pole  in  summer,  while  it  shines  23}^  degrees  beyond 
the  north  pole.  In  winter  these  conditions  are  reversed. 
Though  first  one  pole  and  then  the  other  is  inclined  toward 


184  EXPERIMENTAL   GENERAL    SCIENCE 

the  sun,  the  position  of  the  earth's  axis  does  not  change.  It 
is  the  change  in  relative  position  as  the  earth  travels  around 
the  sun,  that  causes  this  appearance,  and  also  produces  the 
changes  in  the  seasons.  When  the  sun  and  earth  are  in  such 
positions  that  the  sun  is  exactly  overhead  at  the  equator,  its 
farthest  rays  just  reach  both  poles.  At  this  time,  the  days 
and  nights  are  equal  everywhere  on  the  earth.  This  condi- 
tion occurs  twice  every  year,  at  the  vernal  equinox  on  March 
21,  when  spring  begins,  and  at  the  autumnal  equinox  on  Sep- 
tember 23,  when  autumn  begins.  In  spring,  the  sun  appears 
to  pass  north  of  the  equator,  and  at  the  beginning  of  summer 
is  23H  degrees  north  of  it.  Here  it  appears  to  stop  and  turn 
southward  again.  This  point  marks  the  summer  solstice ,  at 
which  time,  in  the  Northern  Hemisphere,  the  days  are  longer 
and  the  nights  shorter  than  at  any  other  time.  The  circle 
over  which  the  sun  appears  to  stop  is  called  the  Tropic  of 
Cancer.  At  this  time,  the  sun's  rays  lack  23}^  degrees  of 
reaching  the  south  pole  and  the  circle  which  they  touch  is 
called  the  Antarctic  circle.  At  the  winter  solstice,  the  sun  is 
23^  degrees  south  of  the  equator  over  the  Tropic  of  Capri- 
corn, and  its  rays  then  just  reach  the  Arctic  Circle  23^  degrees 
from  the  north  pole  (§80). 

Practical  Exercises 

1.  Does  the  size  of  the  circle  make  any  difference  in  the  number  of 
degrees  in  it? 

2.  How  does  the  size  of  a  circle  affect  the  size  of  a  degree? 


3.  What  is  the  great  circle  called  that  is  located  midway  between  the 
poles  of  the  earth? 


4.  In  what  part  of  the  world  is  Greenwich,  from  whose  meridian 
longitude  is  usually  measured? 


LONGITUDE   AND    TIME  185 

5.  What  is  the  number  of  the  meridian  on  the  opposite  side  of  the 
world  from  Greenwich? 


6.  How  does  the  length  of  a  degree  on  any  circle  north  or  south  of  the 
equator  compare  with  a  degree  on  the  equator?     Why? 

7.  Draw  a  circle  and  divide  it  into  4  equal  parts  by  lines  running 
through  its  center.     WThere  the  lines  cross,  four  right  angles  are  formed. 
By  means  of  a  protractor,  find  how  many  degrees  there  are  in  a  right 
angle. 


8.  Draw  a  line  through  your  circle,  making  an  angle  of  45  degrees 
with  a  horizontal  line. 


9.  Draw  a  circle  to  represent  the  earth  and  indicate  by  a  line  the  axis 
tilted  the  proper  number  of  degrees  from  the  perpendicular. 

10.  What  is  the  name  of  the  zone  bounded  by  the  antartic  circle? 

11.  How  many  degrees  are  there  from  the  equator  to  either  pole? 

12.  How  far  north  or  south  of  the  equator  is  the  sun  exactly  overhead 
at  some  time  of  the  year? 

13.  What  zone  do  the  tropics  bound? 

14.  How  many  degrees  wide  is  it? 

15.  How  wide  is  each  frigid  zone? 

16.  How  wide  is  each  temperate  zone? 

17.  If  you  go  to  a  place  where  nothing  obstructs  the  view,  how  many 
degrees  will  there  be  in  your  horizon^. 


186  EXPERIMENTAL   GENERAL   SCIENCE 

18.  How  many  degrees  in  a  line  drawn  from  one  side  of  the  horizon 
to  the  other  through  the  zenitht 

19.  When  the  sun  is  overhead,  how  many  degrees  above  the  horizon 
is  it  at  noon? 

20.  When  the  sun  is  perpendicular  over  the  tropic  of  Capricorn,  how 
high  is  it  at  the  equator  at  noon? 


21.  The  north  pole  points  to  the  north  star.     How  high  would  this 
star  be  if  one  were  at  the  north  pole. 


22.  If  one  should  go  south  to  the  equator,  where  would  the  north 
star  appear? 

23.  If  you  were  in  a  part  of  the  world  where  the  north  star  was  60 
degrees  above  the  horizon,  would  you  be  nearer  the  equator  or  the  pole? 


24.  When  the  sun  is  over  the  equator,  how  high  is  it  in  the  sky  in 
your  region?     What  is  your  latitute? 


25.  How  high  is  the  sun  at  noon  in  your  region  at  the  beginning  of 
whiter?     (Over  what  part  of  the  earth  is  the  sun  perpendicular?) 

26.  How  high  in  the  sky  is  the  sun  at  midsummer? 


27.  What  time  is  it  when  the  sun  crosses  the  meridian  on  the  opposite 
side  of  the  earth  from  you? 


28.  How  long  is  the  longest  period  of  daylight  at  the  equator? 

29.  How  does  this  compare  with  your  own  region? 

30.  What  meridian  determines  the  time  for  yo'ur  locality? 


LONGITUDE    AND    TIME  187 

31.  When  it  is  noon  in  your  time  belt,  is  it  earlier  or  later  than  true  noon 
in  your  own  town? 

32.  Examine  the  globe  for  the  International  Date-line,  where  the  day 
is  assumed  to  begin.     Near  what  meridian  is  it? 

33.  What  advantage  is  there  in  having  the  day  begin  where  it  does? 

34.  Can  you  account  for  the  irregularities  noticed  in  the  date  line? 

35.  Suppose  you  were  traveling  around  the  earth  toward  the  east. 
After  you  had  gone  fifteen  degrees,  would  you  see  the  sun  an  hour  earlier 
or  an  hour  later  than  in  your  first  position. 

36.  Would  you  have  lost  or  gained  an  hour? 

37.  What  would  be  the  gain  or  loss  in  going  entirely  around  the 
earth? 

38.  Suppose  you  had  gone  around  the  earth  toward  the  west.     Would 
you  have  lost  or  gained  a  day? 

39.  The  loss  or  gain  of  a  day  in  going  around  the  earth  is  adjusted 
at  the  international  date-line  by  adding  or  dropping  a  day.     If  you 
should  reach  this  line  on  the  day  before  your  birthday  or  other  holiday, 
which  way  would  you  prefer  to  be  traveling? 

40.  What  would  be  the  effect  if  you  were  traveling  in  the  opposite 
direction? 

41.  Would  this  have  any  effect  on  your  age? 

42.  Can  you  explain  how  it  is  possible  for  an  event  to  happen  on 
Monday  in  Japan  and  be  known  to  us  the  Sunday  before? 

43.  Why  would  a  man  at  the  north  pole  be  unable  to  tell  time  by  the 
sun? 


CHAPTER  XXVII 
MACHINES 

153.  Mechanical  Advantage. — A  machine  is  a  contrivance 
for  transferring  or  transforming  energy,  and  therefore  can 
never  give  out  more  energy  than  is  put  into  it.     A  "  perpetual 
motion"    machine  is  mechanically  impossible.     One  of  the 
advantages  of  a  machine  is  that  it  can  turn  a  small  force  applied 
for  a  long  time  at  one  point  into  a  larger  force  for  a  short 
time  at  some  other  point,  and  thus  a  feeble  force  may  be  made 
to  accomplish  great  things.     By  means  of  a  strong  bar,  we 
may  raise  a  stone  that  we  could  not  move  otherwise.     It 
will  be  noted,  however,  that  the  stone  moves  only  a  few  inches 
while  the  end  of  the  bar  to  which  the  pressure  is  applied  is 
moving  much  farther.     That  is,  a  small  force  acting  through  a 
foot  or  more  has  been  transformed  into  a  greater  force  acting 
through  a  few  inches.     The  force  applied  to  the  machine  is 
called  the  effort,  or  power,  and  the  force  the  machine  exerts  is 
the  resistance  or  weight  overcome.     The  ratio  of  the  resistance 
to  the  effort  gives  the  mechanical  advantage  of  the  machine. 

154.  Simple  Machines. — There  are  but  six  types  of  simple 
machines  in  the  world.     All  more  complex  machines,  whether 
watches,  dynamos,  steam  engines,  automobiles,  or  printing 
presses,   are  merely  combinations  of  these  simple  machines 
which  are  so  familiar  to  us  that  we  scarcely  think  of  them  as 
machines  at  all.     These  simple  machines  are  the  lever,  the 
pulley,  the  wheel  and  axle,  the  inclined  plane,  the  wedge,  and 
the  screw.     As  a  matter  of  fact,  the  principles  upon  which 
they  operate  may  be  further  reduced  to  two — the  lever  and 
the  inclined  plane. 

188 


MACHINES  189 

155.  The  Lever  and  Its  Adaptations. — The  lever  is  a  rigid 
bar,  straight  or  curved,  which  turns  on  an  axis  called  a,  fulcrum. 
The  divisions  of  the  lever  are  called  arms.  If  the  arms  of  a 
lever  are  equal,  a  force  applied  to  one  arm  will  exactly  balance 
an  equal  weight  at  the  other.  The  balances  in  the  chemical 
laboratory  are  of  this  kind.  If  the  arms  are  unequal,  how- 
ever, it  will  be  necessary  to  place  a  larger  weight  on  the  short 
arm  to  balance  a  given  weight  on  the  long  arm.  The  old- 
fashioned  steelyards  and  all  platform  scales  are  of  this  type. 
A  general  law  of  mechanics  is  that  the  power  multiplied  by 
its  distance  from  the  fulcrum  is  equal  to  the  weight  mul- 
tiplied by  its  distance  from  the  same  point.  Thus,  10  pounds 
on  the  arm  of  a  lever  5  inches  long  will  just  balance  a  weight 
of  5  pounds  on  an  arm  10  inches  long.  There  are  three  classes 
of  levers.  In  levers  of  the  first  class,  the  fulcrum  is  between 
the  power  and  the  weight,  as  in  the  balanced  scales  of  the 
merchant.  In  levers  of  the  second  class,  the  weight  is  between 
the  power  and  the  fulcrum,  as  when  we  move  an  object  by 
lifting  on  a  bar  the  other  end  of  which  rests  on  the  ground 
beneath  it.  In  levers  of  the  third  class,  the  weight  is  at  one 
end,  the  fulcrum  at  the  other,  and  the  power  applied  in  the 
middle,  as  in  the  treadle  of  most  foot-power  machines.  The 
wheel  and  axle  may  be  considered  as  an  adaptation  of  the  lever 
—what  might  be  called  a  lever  arm  revolving  about  a  fulcrum. 
The  mechanical  advantage  in  this  type  of  machine  is  found  in 
the  ratio  that  the  circumference,  the  diameter,  or  the  radius 
of  the  wheel  bears  to  the  circumference,  diameter,  or  radius 
of  the  axle.  Thus,  if  the  diameter  of  a  wheel  is  twice  that  of 
the  axle,  the  force  applied  to  the  wheel  will  lift  twice  as  much 
as  if  .applied  to  the  axle.  The  pulley  may  be  considered 
another  adaptation  of  the  lever,  the  shaft  on  which  the 
pulley  is  fixed  being  the  fulcrum.  The  rope  running  over  the 
pulley  acts  as  a  balance  lever,  since  any  force  pulling  down  on 
one  end  will  exactly  balance  an  equal  weight  on  the  other.  If 


190  EXPERIMENTAL   GENERAL   SCIENCE 

one  end  of  a  rope  be  fastened  to  a  support,  however,  and  then 
carried  over  a  free  pulley  to  which  a  weight  is  attached,  a 
pull  upward  of  25  pounds  will  lift  a  50-pound  weight,  but  the 
rope  will  move  twice  as  far  as  the  weight  is  lifted.  The  power 
or  effort  necessary  to  move  a  given  weight  by  the  use  of  a 
pulley  may  therefore  be  diminished  by  introducing  one  or 
more  free  pulleys  over  which  the  rope  runs.  In  other  words 
the  power  is  multiplied  as  many  times  as  the  rope  passes  over 
the  movable  pulley,  or  pulleys  thus  introduced.  The  distance 
through  which  the  rope  must  move,  however,  is  also  multi- 
plied in  proportion  to  the  distance  traversed  by  the  weight 
lifted. 

156.  The  Inclined  Plane  and  Its  Adaptations. — The  second 
type  of  the  simple  machine  is  the  inclined  plane.     In  this  the 
mechanical  advantage  is  the  ratio  of  the  length  of  the  plane 
to  its  height.     For  instance,  it  will  take  only  one-half  as  much 
effort  to  roll  a  barrel  up  a  plane  8  feet  long  into  a  wagon  4 
feet  high,  as  it  would  to  lift  the  barrel  directly  into  the  wagon, 
but  though  the  force  in  this  instance  is  only  half  as  great,  it 
travels  twice  as  far.     The  wedge  is  a  form  of  the  inclined  plane 
which  is  pushed  under  the  load  instead  of  the  load  being  moved 
upon  it.     Its  mechanical  advantage  is  exactly  like  that  of  the 
inclined  plane.     The  screw  may  be  regarded  as  an  inclined 
plane  winding  about  a  cylinder.     The  distance  between  any 
two  adjoining  threads  is  called  the  pitch.     Screws  when  used 
as  machines,  usually  work  with  a  lever.     The  mechanical 
advantage  in  the  screw  is  found  to  be  the  ratio  of  the  distance 
traveled  by  the  power  (end  of  the  lever)  to  the  pitch  of  the 
screw.     If  the  pitch  is  Y±  inch  and  the  lever  travels  in  a  circle 
3  feet  in  circumference,  the  ration  would  be  144  (3  X  12  X  4) 
to  1,  and  a  force  of  10  pounds  applied  on  the  lever  would  lift 
a  weight  of  1440  pounds  on  the  screw. 

157.  The    Hydraulic    Press. — The    hydraulic    press    is    a 
machine   by  means  of  which  a  man  is  able  to  exert  many 


MACHINES 


191 


thousands  of  pounds  pressure  with  what  appears  to  be  a  very 
small  effort.  The  machine  consists  essentially  of  two  connect- 
ing cylinders  of  unequal  diameters  filled  with  water.  When 
pressure  is  applied  to  the  water  in  the  small  cylinder,  it  is 
transmitted  to  the  large  cylinder  where  it  is  multiplied  as 
many  times  as  the  cross-sectional  area  of  the  large  cylinder  is 
greater  than  that  of  the  smaller  one.  At  the  same  time  the 
general  law  of  machines  holds  good,  for  the  piston  in  the  small 
cylinder  moves  as  many  times  as  far  as  the  effort  is  multiplied. 


FIG.  64. — Cross-section  of  a  hydraulic  press.     (Tower,  Smith  and  Turton.) 

Suppose  a  large  cylinder  to  have  an  area  of  1000  times  that 
of  the  small  one.  Then  one  pound  pressure  in  the  small 
cylinder  would  give  1000  pounds  pressure  in  the  other,  but  the 
piston  in  moving  the  1000  pounds  one  inch  would  have  to 
travel  a  thousand  inches.  By  making  the  pressure  a  hundred 
pounds  in  the  small  cylinder,  it  would  have  to  travel  10  inches 
for  each  inch  the  thousand  pounds  was  moved.  Hydraulic 
presses  are  often  used  to  compress  coarse  materials  such  as 
paper,  shavings,  cotton,  and  the  like.  Some  elevators  are 
also  run  by  hydraulic  pressure. 


192 


EXPERIMENTAL   GENERAL   SCIENCE 


Practical  Exercises 

1.  If  a  weight  of  25  pounds  be  placed  on  one  arm  of  a  lever  10  inches 
long,  how  far  from  the  fulcrum  must  a  10-pound  weight  be  placed  on  the 
other  arm  to  exactly  balance  it? 


2.  A  meter  stick  has  a  fulcrum  placed  under  it,  exactly  20  centimeters 
from  one  end.     On  this  end  a  weight  of  100  grams  is  placed.     How 
many  grams  must  be  placed  on  the  other  end  to  balance 
it? 


\ 


p  if  5 


3.  Two  boys  make  a  see-saw  of  a  long  plank.     If  one 
boy,  who  weighs  70  pounds,  sits  eight  feet  from  the  fulcrum , 
at  what  distance  must    the   other   boy,  who  weighs  56 
pounds,  sit  to  exactly  balance  the  see-saw? 

4.  A  man  wishes  to  lift  a  stone  by  bearing  down  with 
his  whole  weight  on  a  crowbar  4  feet  long.     How  much  can 
he  lift  if  he  weighs  150  pounds  and  the  fulcrum  of  his  lever 
is  three  inches  from  the  end  of  the  bar? 


6.  Write  opposite  the  following  names  the  class  of  lever 
to  which  each  belongs:  a  pair  of  scissors,  a  pump,  a  wheel- 
barrow, a  pair  of  tweezers,  a  bellows,  a  spade,  a  door,  a 
nut-cracker,  a  clawhammer. 


6.  A  windlass  with  a  crank  2  feet  long  is  used  to  lift  ore 


ou*  °^  a  mme-    K  an  en?°rt  of  50  pounds  is  applied  to  the 
crank,  how  much  ore  can  be  lifted  at  a  time  if  the  lifting 
rope  winds  up  on  an  axle  6  inches  in  diameter? 


7.  A  bucket  of  water  weighing  72  pounds  is  to  be  lifted  by  a  windlass 
with  an  axle  6  inches  in  diameter  and  a  crank  18  inches  long?  How 
much  force  must  be  applied  continually  to  the  crank  to  do  the  work? 


8.  Study  the  accompanying  illustration  and  decide  how  many  pounds 
pull  on  the  rope  will  lift  a  100-pound  weight? 


MACHINES  193 

9.  How  far  must  the  rope  be  pulled  to  lift  the  weight  three  feet? 

10.  How  much  force  is  needed  to  move  a  200-pound  load  up  an  incline 
1000  feet  long  and  50  feet  high? 

11.  A  man  lifts  a  box  weighing  100  pounds  into  a  doorway  3  feet  high. 
How  much  power  would  he  have  needed  to  move  the  box  up  an  inclined 
board  6  feet  long? 

12.  How  much  force  would  have  been  required  if  the  board  mentioned 
in  question  11,  were  twelve  feet  long? 

13.  How  much  will  a  jack-screw  lift  if  it  has  a  pitch  of  %  inch  and  is 
operated  by  a  bar  two  feet  long  to  which  a  force  of  100  pounds  is  applied? 

14.  Opposite  the  names  in  the  following  list  write  the  name  of  the 
machine  it  represents :  a  chisel,  an  axe,  a  grindstone,  a  propeller,  a  wheel- 
barrow, an  electric  fan. 


15.  Why  may  the  pressure  of  pushing  a  cork  into  a  large  bottle  cause 
it  to  break? 


ia 


CHAPTER  XXVIII 


MAGNETISM 

158.  The  Lodestone. — Many  centuries  ago  it  was  discovered 
that  a  certain  kind  of  iron  ore  had  the  curious  property  of 
attracting  other  small  pieces  of  iron.  Ore  of  this  kind  is 
found  in  many  parts  of  the  world,  and  is  commonly  known  as 
magnetite.  If  a  piece  of  it  be  dipped  into  iron  filings,  they 
will  cling  to  it,  and  tacks,  small  nails,  and  other  small  objects 
of  iron  or  steel,  may  be  picked  up  in  this  way.  Pieces  of  this 
ore  were  once  called  lodestones,  or  lead- 
ing stones,  but  since  the  first  were  found 
near  Magnesia  in  Asia  Minor,  they  have 
finally  come  to  be  called  magnetic  stones 
of  natural  magnets.  A  piece  of  steel,  such 
as  a  knife  blade  or  needle,  may  be  mag- 


FIG.  66. — Magnets.      (Tower,  Smith  and  Turton.) 

netizedj  or  given  magnetic  properties,  by  stroking  it  with  a 
natural  magnet,  and  it  will  then  have  all  the  properties  of  the 
original  magnet.  Artificial  magnets,  made  in  other  ways,  are 
now  very  common  and  are  indispensable  in  electrical  work. 
In  artificial  magnets,  the  most  common  are  bar  magnets, 
made  of  straight  pieces  of  steel,  and  horseshoe  magnets,  whose 
name  is  suggested  by  their  shape.  Steel,  when  magnetized, 
becomes  a  permanent  magnet,  but  soft  iron  can  be  magnetized 
only  temporarily.  When  a  magnet  is  hammered,  heated,  or 
twisted,  it  loses  its  magnetism. 

194 


MAGNETISM  195 

159.  Poles  of  the  Magnet. — If  a  lodestone  be  dipped  into 
iron  filings,  it  will  be  found  that  there  are  two  places  on  its 
surface  where  the  filings  seem  to  be  held  with  greater  force 
than  elsewhere,  and  this  condition  is  also  found  to  exist  in  all 
artificial  magnets.     When  any  magnet  is  hung  up  in  such  a 
way  that  it  is  free  to  turn  in  any  direction,  it  soon  assumes  a 
general  north  and  south  position  and,  when  pushed  out  of 
this  position,  it  returns  to  it  as  soon  as  released.     This  shows 
that  the  position  assumed  is  not  accidental,  and  indicates  the 
existence  of  some  sort  of  force  affecting  it.     The  end  of  the 
magnet  which  thus  invariably  turns  toward  the  north  is  called 
the  north-seeking  pole,  or  simply  the  north 

pole,  while  the  opposite  end  is  the  south 
pole.  On  many  magnets,  the  poles  are  in- 
dicated by  the  letters  "  N  "  and  "  S  "  stamped 
upon  them.  The  poles  of  a  magnet  agree 
with  the  points  on  its  surface  which  attract 
iron  most  strongly.  FlG  67  _A  mag. 

160.  The  Earth  a  Magnet. — The  earth    netoscope.     (Tower, 
itself  appears  to  be  a  great  magnet  with  one    ' 

pole  near  the  geographical  north  pole,  and  another  in  the 
southern  hemisphere  on  the  opposite  side  of  the  earth.  It  is 
to  this  magnetic  north  pole,  rather  than  to  the  geographical 
north  pole,  that  the  magnet  turns.  This  pole  is  west  of 
Baffins  Bay,  but  its  position  varies  somewhat.  In  consequence, 
there  are  many  places  in  the  United  States  where  magnets  do 
not  point  due  north  and  south  if  allowed  to  swing  free.  In 
surveying  and  other  work  depending  on  the  use  of  the  com- 
pass, allowance  must  therefore  be  made  for  this  difference. 

161.  The  Compass. — The  compass  is  simply  a  magnetized 
needle  so  mounted  as  to  move  freely  in  a  horizontal  circle 
and  thus  indicate  by  its  position  the  direction  of  the  north 
magnetic  pole.     A  true  north  and  south  line  is  then  easy  to 
establish  by  making  proper  allowance  for  the  difference  be- 


196 


EXPERIMENTAL  GENERAL   SCIENCE 


tween  the  true  north  pole  and  the  one  toward  which  the  needle 
points.  A  magnetized  needle  mounted  to  swing  in  a  perpen- 
dicular circle  is  called  a  dip-needle. 
When  a  dip-needle  is  carried  toward 
the  north  magnetic  pole,  its  north 
pole  begins  to  dip  downward  and,  at 
the  pole,  assumes  a  perpendicular 
position.  The  magnetic  pole  may 
therefore  be  located  either  by  the 
dip-needle  or  the  compass. 

162.  Lines  of  Force. — If  a  piece  of 
paper  be  laid  over  a  magnet  and  iron 

filings  sprinkled  upon  it,  a  gentle  tapping  of  the  paper  will 
cause  the  filings  to  arrange  themselves  in  curious  patterns, 
which  indicate  the  lines  of  force  proceeding  from  the  magnet. 


FIG.  69. — Iron  filings  showing  lines  of  force  about  a  bar  magnet.     (Tower, 
Smith  and  Turton.) 

It  will  be  seen  that  these  lines  tend  to  circle  around  from  one 
pole  to  the  other.  The  arrangement  of  the  filings  is  due  to 
the  fact  that  each  particle  is  for  the  time  a  magnet,  and  takes 


MAGNETISM  197 

the  position  that  a  compass  needle  would  in  the  same  situa- 
tion. These  invisible  lines  of  force  explain  how  a  magnetic 
body  may  affect  another  without  being  brought  into  actual 
contact  with  it.  As  would  be  expected,  the  further  apart 
such  bodies  are,  the  less  will  be  the  effect.  When  a  body  not 
naturally  a  magnet  is  given  magnetic  properties  by  contact 
with  a  magnet,  it  is  said  to  be  magnetized  by  induction. 

Practical  Exercises 

1.  Carefully  place  a  sewing  needle  on  the  surface  of  a  basin  of  water. 
Does  it  come  to  rest  in  any  definite  position?     Make  three  trials. 


2.  Gradually  bring  one  end  of  a  bar  magnet  toward  the  needle.     How 
does  the  latter  behave? 


3.  Present  the  other  end  of  the  magnet  to  the  needle.     What  result? 

4.  Magnetize  the  needle  just  used  by  stroking  it  several  times  in  one 
direction  with  one  end  of  the  bar  magnet.     Place  on  the  surface  of  a 
basin  of  water  at  some  distance  from  any  iron.     In  what  position  does 
the  needle  now  come  to  rest?     (Make  several  trials.) 

5.  Repeat  experiments  2  and  3  with  this  needle.     What  is  the  result? 


6.  Slowly  bring  the  north  pole  of  a  bar  magnet  toward  the  north  pole 
of  a  compass.     What  is  the  result? 


7.  Repeat  the  foregoing  experiment  with  the  south  pole  of  the  magnet. 
Can  magnets  repel  as  well  as  attract? 


8.  Do  like  or  unlike  poles  attract? 

9.  If  we  call  the  end  of  the  magnet  which  points  to  the  north  the 
north  pole,  is  the  north  magnetic  pole  a  north  or  a  south  pole? 


198  EXPERIMENTAL   GENERAL  SCIENCE 

10.  Dip  a  piece  of  soft  iron  rod  or  wire  into  some  iron  filings.     Is  soft 
iron  magnetic? 


11.  Hold  one  end  of  a  bar  magnet  against  an  iron  rod  and  dip  the 
opposite  end  of  the  rod  in  iron  filings.  How  does  the  magnet  affect  the 
rod? 


12.  Remove  the  magnet.     What  effect  has  this  on  the  magnetism  in 
the  rod? 


13.  If  two  bar  magnets  are  to  be  kept  in  a  box,  how  should  they  be 
placed  with  respect  to  each  other? 


14.  An  iron  bar  or  pipe  that  has  stood  in  an  erect  position  for  some  time 
comes  to  have  magnetic  properties.     By  means  of  a  compass,  test  such 
an  object  and  discover  which  end  is  a  north  pole. 

15.  Sprinkle  some  iron  filings  on  a  sheet  of  paper  or  glass  and  slowly 
move  a  bar  magnet  beneath.     Make  the  same  experiment  with  the  filings 
on  a  sheet  of  iron.     Which  of  these  substances  is  the  best  screen  for 
magnetic  action? 


16.  Which  is  the  best  test  for  a  magnetized  body,  that  it  is  attracted 
by  a  magnet  or  repelled?     Why? 


17.  The  Carnagie,  a  ship  for  making  magnetic  observations,  is  con- 
structed without  iron.     Of  what  advantage  is  this? 


18.  Why  would  a  compass  be  unreliable  near  a  mountain  of  iron 
ore? 


CHAPTER  XXIX 
STATIC  ELECTRICITY 

163.  Electricity  by  Friction. — If  a  fountain  pen,  comb,  or 
other  object  made  of  rubber,  or  an  ebonite  rod,  be  rubbed 
rapidly  with  a  piece  of  woolen  cloth  such  as  a  coat  sleeve,  the 
object  will  attract  small  bits  of  paper,  shavings,  and  the  like, 
exactly  as  a  magnet  picks  up  bits  of  iron  and  steel.  A  similar 
effect  may  be  seen  when  a  sheet  of  paper  is  warmed  and  rubbed 


FIG.  70.— The  Toeppler-Holtz  induction  machine.     (Tower,  Smith 
and  Turton.) 

vigorously  with  the  hand  or  a  woolen  cloth.  It  will  then 
attract  other  bits  of  paper,  or  cling  to  the  wall  or  door  if  pressed 
against  it.  Sometimes  the  rubbing  in  this  way  may  even 
produce  a  spark,  as  when  one  combs  the  hair  with  a  rubber 
comb,  or  strokes  a  cat  on  a  cold  dry  day.  By  scuffling  about 
on  a  thick  carpet,  one  may  sometimes  produce  a  spark  large 
enough  to  light  the  gas  when  it  is  touched  by  the  finger. 

199 


200 


EXPERIMENTAL   GENERAL    SCIENCE 


Bodies  which  behave  in  this  way  when  rubbed  are  said  to  be 
electrified  or  charged.  In  many  ways,  magnetized  and  elec- 
trified bodies  are  alike,  but  they  differ  in  one  important  par- 
ticular. While  almost  any  object  may  be  electrified,  only 
three  common  substances — iron,  cobalt,  and  nickel — can  be 
magnetized. 

164.  Two  Kinds  of  Electricity. — When  two  bodies  are 
electrified  in  the  same  manner,  they  act  like  similar  poles  of 
two  different  magnets — that  is,  they  repel  each  other.  This 


[EH 


FIG.    71.— Pith  ball   attracted  by  electrified  rod, 
but  when  electrified,  repelled  by  it. 


FIG.  72.— Pith  balls 
with  like  charges  repel 
each  other. 


can  easily  be  shown  by  suspending  tiny  balls  of  cork,  pith, 
or  cotton  by  silk  threads  and  testing  them  with  some  electri- 
fied object,  such  as  a  fountain  pen  or  an  ebonite  rod  rubbed 
with  a  woolen  cloth.  If  the  object  is  brought  toward  the  ball 
before  it  is  electrified,  no  change  is  noted,  but  when  it  is 
electrified  the  ball  is  first  attracted  by  it  and  then  as  strongly 
repelled.  If  the  same  experiment  be  now  performed  with 
electricity  obtained  by  rubbing  a  warm  glass  rod  with  a  piece 
of  silk,  the  balls  behave  as  before,  being  first  attracted  by  the 
rod  and  then  repelled.  But  while  two  balls  charged  from 


STATIC   ELECTRICITY  201 

either  an  ebonite  rod  or  a  glass  rod,  repel  each  other,  a  ball 
charged  from  a  glass  rod  will  attract  one  charged  from  an 
ebonite  rod.  This  shows  clearly  that  there  are  two  kinds  of 
electricity,  and  that,  as  in  magnetism,  like  charges  repel  and 
unlike  charges  attract.  The  electricity  produced  on  glass 
is  known  as  positive  (+)  electricity  and  that  produced  on 
rubber  is  negative  (  — )  electricity.  These  two  kinds  of  elec- 
tricity appear  to  be  so  evenly  balanced  on  all  objects-,  that  one 
cannot  be  produced  without  the  other.  When  an  ebonite 
rod  is  rubbed  with  a  woolen  cloth,  for  instance,  negative  elec- 
tricity is  developed  on  the  rod,  but  positive  electricity  is 
developed  on  the  cloth.  It  should  be  noted  that,  unlike  mag- 
netism, electrification  is  not  more  effective  at  one  point  on  an 
object  than  another.  It  seems  to  be  evenly  distributed  over 
the  surface  of  an  electrified  body  and  may  be  removed  at  any 
point.  Smooth  surfaces  prevent  the  escape  of  electricity 
much  as  they  prevent  the  escape  of  heat.  A  series  of  points 
is  always  most  effective  in  discharging  an  electrified  body. 

165.  The  Electroscope. — Taking  advantage  of  the  fact  that 
like  charges  repel,  it  is  easy  to  construct  a  device  that  will 
show  when  a  body  is  electrified.  Such  a  device  is  called  an 
electroscope.  Two  pith  balls  attached  to  a  common-  support 
by  silk  thread  will  serve  the  purpose,  but  the  more  usual  form 
consists  of  two  strips  of  gold  or  aluminum  foil  attached  to  a 
metal  rod  and  enclosed  in  a  glass  flask  to  protect  the  delicate 
strips  of  foil.  The  rod  is  supported  by  a  cork  in  the  neck  of 
the  flask.  When  an  electrified  body  is  brought  toward  the 
electroscope,  it  becomes  charged  by  induction,  as  it  is  called, 
and  the  strips  of  foil  or  the  pith  balls  spread  apart  in  con- 
sequence. When  the  electrified  body  is  withdrawn,  they  fall 
together  again.  If,  however,  one  touches  the  electroscope 
while  the  leaves  are  still  separated,  withdrawing  the  electri- 
fied body  does  not  cause  the  leaves  to  fall  together  again, 
because  one  kind  of  electricity  (the  opposite  of  the  one  on  the 


202  EXPERIMENTAL  GENERAL   SCIENCE 

charged  body)  has  flowed  away  to  the  earth  as  soon  as  touched. 
There  is  left  in  the  electroscope,  therefore,  only  one  kind  of 
electricity  which  causes  the  strips  of  foil  to  repel  one  another, 
and  until  enough  of  the  other  kind  of  electricity  can  return  to 
the  electroscope  and  balance  the  charge  it  contains,  the  strips 
of  foil  must  continue  to  be  separated.  This  return  of  elec- 
tricity is  prevented  by  the  glass  case  through  which  it  can 
not  pass. 

166.  Insulators. — Substances  which,  like  glass,  prevent  the 
passage  of  electricity  are  called  insulators.     Glass  is  one  of  the 
best  of  insulators.     Others  are  silk,  amber,  sulphur,  rubber, 
and  dry  air.     Metals  and  other  good 
conductors  of  heat  are  also  good  con- 
ductors of  electricity.     Water  is  ordi- 
narily a  poor  conductor,  but  when  salts 
are  dissolved  in  it,  it  becomes  a  good 
conductor.     Substances  that  are  ordi- 
narily good  insulators  may  become  con- 
ductors when  wet. 
FIG.    34.— Leyden    jar      167.  The  Leyden  Jar. — A  glass  jar 

and  discharger.  (Tower,  with  th  lower  hajf  CQated  inside  and 
Smith  and  Turton.) 

out  with  tinfoil  is  known  as  a  Leyden 

jar.  A  metal  rod  held  in  place  by  an  insulator  extends  down 
inside  of  the  jar  and  in  contact  with  the  lining.  When  the 
knob  at  the  top  of  the  metal  rod  is  charged  with  positive 
electricity,  it  repels  the  positive  electricity  on  the  outside  of 
the  jar,  which  is  at  once  conducted  from  the  jar  to  the  earth 
through  the  jar's  support.  After  a  time  the  jar  becomes  fully 
charged  and  will  then  receive  no  more  electricity.  It  now  has 
a  charge  of  positive  electricity  on  its  inner  surface  and  a  like 
charge  of  negative  electricity  on  its  outer  surface.  If  the  two 
surfaces  are  then  nearly  connected  by  means  of  a  wire,  the  jar 
is  then  discharged  with  a  bright  spark  and  crackling  noise.  Such 
jars  and  other  similar  structures  are  often  known  as  condensers. 


STATIC   ELECTRICITY  203 

168.  Lightning. — A  lightning  flash  is  simply  a  large  spark 
similar  to  that  produced  by  the  discharge  of  the  Ley  den  jar. 
When  two  clouds  charged  with  electricity  approach  each  other, 
they  may  act  as  the  coats  of  a  huge  Ley  den  jar,  the  air  between 
acting  like  the  glass.  When  the  charge  breaks  through  the 
air  from  one  cloud  to  another,  a  lightning  flash  is  the  result. 
Sometimes  the  earth  and  a  cloud  act  as  the  two  coats  of  a 
jar,  and  then  we  may  have  a  stroke  of  lightning.  Tall  objects, 
such  as  chimneys,  trees,  and  towers  act  as  the  wire  did  in 
discharging  the  Ley  den  jar,  and  are  thus  often  said  to  attract 
the  lightning.  Heat  lightning,  often  seen  near  the  horizon 
on  summer  evenings,  is  simply  the  reflection  of  the  lightning 
from  thunder  storms  too  distant  for  the  thunder  to  be 
heard.  The  Aurora  Borealis,  or  northern  lights,  is  now  re- 
garded as  being  caused  by  the  passage  of  electric  currents  far 
above  the  earth. 

Practical  Exercises 

1.  Why  are  electrical  push  buttons  and  switches  usually  made  of 
rubber  or  gutta-percha? 


2.  The  wires  used  for  electric  wiring  in  houses  are  covered  with  a 
layer  of  rubber  or  silk  thread  or  by  both.     Of  what  use  is  this? 


3.  Does  a  charged  body  attract  or  repel  one  not  charged? 

4.  Hang  up  two  balls  of  pith  or  cotton  by  means  of  silk  thread  and 
charge  from  any  convenient  source.     Thoroughly  wet  one  of  the  silk 
threads  and  again  charge.     Which  retains  its  charge  best?     Why? 


5.  Why  could  not  wire  be  used  as  well  as  silk  for  suspending  the  pith 
balls? 


6.  When  a  large  belt  runs  over  a  pulley,  one  may  often  draw  a  good- 
sized  spark  from  it  by  merely  touching  it  with  a  piece  of  metal.     Explain. 


204  EXPERIMENTAL   GENERAL   SCIENCE 

7.  In  wet  weather  one  may  often  get  a  shock  by  touching  a  tree  with 
which  an  electric  wire  is  in  contact.  Why  is  a  shock  not  as  likely  on  a 
dry  day? 


8.  Is  it  possible  for  a  lightning  flash  to  move  from  the  earth  to  a  cloud 
instead  of  the  reverse? 


9.  Why  is  a  lightning  stroke  likely  to  run  along  a  wire  instead  of 
taking  a  more  direct  path  to  the  ground? 


10.  Why  are  the  supports  for  electric  wires  made  of  glass  or  porcelain? 

11.  Why  do  electric  linemen  wear  rubber  gloves  while  at  work? 

12.  If  one  had  to  move  a  naked  wire  known  to  be  carrying  electricity, 
which  would  be  better  to  use,  a  glass  or  a  metal  rod? 

13.  Why  is  a  cold  dry  day  best  for  electric  experiments? 

14.  Why  will  a  Leyden  jar  fail  to  be  charged  if  placed  on  glass? 

15.  Hold  a  piece  of  glass  between  the  points  of  discharge  on  a  friction 
electric  machine.     How  do  electricity  and  magnetism  compare  as  to  the 
ease  with  which  they  pass  through  glass? 

16.  Why  should  a  lightning  rod  be  "grounded"  by  being  carried  down 
to  permanently  moist  soil? 


CHAPTER  XXX 
CURRENT  ELECTRICITY 

169.  Useful  Electricity. — Static   electricity,    produced    by 
rubbing  one  body  with  another,  though  important  in  some 
respects,  is  not  capable  of  doing  useful  work.     Even  when   it 
is  accumulated  on  a  condenser,  such  as  a  Ley  den  jar,  the 
discharge   is  practically  instantaneous,   while  for  operating 
machinery  and  the  like,  a  continuous  flow  of  electricity  is 
required.     The  current  electricity  now  so  extensively  used, 
was  not  known  until  long  after  the  effects  produced  by  static 
electricity  were  familiar  to  scientists ;  but  until  its  discovery, 
no  progress  in  adapting  electricity  to  manufacturing,  trans- 
portation, and  the  like  was  possible. 

170.  The  Voltaic  Cell. — The   first    current  electricity  was 
produced  by  chemical  energy.     It  was  found  that  when   a 
strip  of  copper  and  a  strip  of  zinc  were  placed  in  a  jar  of  water 
containing  a  small  amount  of  sulphuric  acid  and  their  pro- 
jecting ends  connected  by  means  of  a  wire,  a  weak  current 
of  electricity,  produced  by  chemical  reaction  between  the 
acid  and  zinc,  would  flow  along  the  wire.     Such  an  arrange- 
ment was  called  a  Voltaic  cell.     Other  metals  and  non-metals 
may  be  used  in  place  of  the  strips  of  copper  and  zinc,   and 
various  other  solutions  may  be  substituted  for  the  dilute 
sulphuric  acid,  but  the  result  is  the  same  in  all,  namely,  the 
transformation  of  chemical  energy  into  a  current  of  electricity. 
Such  cells  are  still  used  for  supplying  the  current  that  rings 
door-bells   and   operates   telegraph  instruments,   telephones, 
and  the  like.     The  most  familiar  form  is  the  dry  cell  which 
consists  of  a  zinc  cup  filled  with  moist  chemicals  surrounding  a 

205 


206 


EXPERIMENTAL   GENERAL   SCIENCE 


carbon  rod.  The  zinc  cup  takes  the  place  of  the  zinc  strip 
in  the  Voltaic  cell,  and  the  carbon  rod  takes  the  place  of  the 
copper. 

171.  Direction  of  the  Current. — The  two  strips  of  metal  in 
the  Voltaic  cell  are  called  the  electrodes,  or  poles,  and  the  liquid 
in  which  they  are  placed,  is  the  electrolyte.  The  zinc  is  called 
the  negative  pole,  and  the  copper  is  the  positive  pole.  The 
electric  current  is  supposed  always  to  flow  from  the  positive 
to  the  negative  pole  in  the  current  through  the  wire  and  from 


FIG.  74.— The  gravity  cell.     (Tower, 
Smith  and  Turton.) 


FIG.  75. — The  Leclanche  cell, 
"dry"  type.  (Tower,  Smith  and 
Turton.) 


the  zinc  pole  to  the  copper  pole  through  the  electrolyte  to 
the  starting  point.  So  long  as  the  two  poles  are  connected, 
the  current  continues  to  flow  and  the  circuit  is  said  to  be  closed. 
If  an  electric  bell  be  connected 'into  the  circuit  it  will  ring, 
or  an  electric  light  may  be  made  to  glow.  When  the  circuit 
is  broken  at  any  point,  the  current  ceases. 

172.  Induced  Currents. — Electricity  produced  by  chemical 
means  is  too  expensive  for  the  thousand  purposes  to  which 
electricity  is  now  put.  The  current  used  for  moving  street 


CURRENT  ELECTRICITY  207 

cars,  elevators,  railway  trains,  and  other  machinery  is  gen- 
erated in  another  way.  When  a  wire  moves  through  a 
magnetic  field,  cutting  the  lines  of  force,  a  current  is  generated 
in  the  wire.  The  amount  of  this  current  depends  upon  the 
strength  of  the  field,  the  speed  of  the  wire,  and  the  number  of 
turns  in  the  latter.  The  electric  dynamo  is  a  machine  for 
revolving  coils  of  wire  in  such  a  field.  It  is  usually  run  by 
steam  or  water  power.  Our  houses  are  lighted  by  currents  of 
electricity  induced  by  the  powerful  currents  passing  along 
the  service  wire,  the  induction  taking  place  in  the  transformer. 

173.  Electroplating. — When  a  current  of  electricity  is  passed 
through  a  solution,  it  decomposes  it  by  electrolysis.     In  this 
way,  water  may  be  decomposed  into  hydrogen  and  oxygen, 
and  melted  table  salt  decomposed  into  the  metal  sodium  and 
chlorine  gas.     Electroplating  is  based  on  the  same  principle. 
The  articles  to  be  plated  are  attached  to  the  positive  pole  of 
the  battery  and  the  piece  of  metal  to  be  used  in  plating,  either 
serves  as  the  other  pole  or  is  attached  to  it.     The  electrolyte 
must  also  contain  some  of  the  metal.     When  the  current  is 
passed  through  the  solution,  small  particles  of  the  metal  are 
carried  across  the  solution  and  deposited  on  the  articles  to  be 
plated.     In   this  way,  iron   is   " galvanized"  with    zinc    or 
covered  with  tin,  and  brass  and  other  metals  plated  with 
nickel,  silver,  or  gold.     In  electrotyping,  an  impression  of  the 
type  is  taken  in  wax  and  a  thin  plating  of  copper  is  deposited 
on  the  wax,  after  which  it  is  backed  with  type  metal.     Since 
wax  is  not  a  good  conductor  of  electricity,  the  mould  must  be 
carefully  dusted  with  powdered  graphite  before  the  work  be- 
gins in  order  to  make  a  connected  circuit.     Gold,  copper,  and 
silver  are  sometimes  separated  from  their  ores  by  electrolysis. 

174.  Electromagnets. — If  a  current  of  electricity  be  sent 
along  a  coiled  wire,  the  wire  acts  like  a  natural  magnet,  and, 
if  hung  up  and  allowed  to  swing  free,  will  assume  a  general 
north  and  south  direction.     By  slipping  into  the  coil  a  piece 


208 


EXPERIMENTAL   GENERAL   SCIENCE 


of  soft  iron,  called  a  core,  the  magnetic  force  of  both  coil  and 
iron  are  greatly  increased,  and  the  effects  continue  as  long  as 
the  current  is  flowing.  When  the  current  ceases,  the  iron  is 
no  longer  magnetic.  Magnets  made  in  this  way  are  called 
electromagnets.  The  most  common  form  is  of  the  familiar 
horseshoe  shape.  Such  magnets  are  an  essential  part  of 
our  electric  bells,  annunciators,  telephones,  and  telegraph 
instruments.  Electric  cranes,  consisting  of  powerful  electro- 
magnets, are  used  for  lifting  heavy  pieces  of  steel  and  iron 
in  mills  and  factories.  The  electric  bell  is  made  to  ring  by 


FIG.    76. — Diagram    of   an 

electroscope.     (Tower,    Smith 
and  Turton.) 


FIG.  77. — An  electric  bell  and  its  circuit- 
A,  Armature;  M,  electromagnet.  (Tower, 
Smith  and  Turton.) 


a  device  that  alternately  makes  and  breaks  the  current  flowing 
through  an  electromagnet  of  horseshoe  form.  A  piece  of  soft 
iron,  called  the  armature,  opposite  the  poles  of  the  magnet 
is  attached  to  the  hammer  of  the  bell,  and,  when  not  in  action, 
a  spring  holds  it  away  from  the  magnet  and  in  contact  with  the 
wire  from  one  pole  of  the  cell  or  battery.  When  the  circuit  is 
closed,  the  current  of  electricity  passes  by  way  of  the  armature 
through  the  coils  of  wire  in  the  horseshoe  making  it  an  electro- 
magnet, and  this  at  once  attracts  the  armature  and  causes 
a  stroke  of  the  bell.  The  motion  of  the  armature,  however, 


CURRENT   ELECTRICITY 


209 


breaks  the  circuit,  the  magnet  ceases  to  act,  and  the  spring 
forces  the  armature  back  into  its  original  position,  where  it 
again  closes  the  circuit  and  causes  the  process  to  be  repeated 
again  and  again. 

175.  Electric  Light  and  Heat. — There  is  no  substance  known 
which  will  conduct  electricity  without  offering  some  resistance 
to  its  passage.  Good  conductors,  therefore,  are  simply 
those  that  offer  the  least  resistance.  The  size  of  the  conduct- 
ing body  also  has  an  effect  on  the  resistance,  for  the  smaller 


.   FIG.  78. — Electric  generator. 

the  wire  the  greater  the  resistance.  Since  heat  develops  as 
the  result  of  resistance,  a  smaller  wire  may  be  heated  white 
hot  by  this  means,  as  for  example  in  the  filament  of  the  in- 
candescent lamp.  When  it  is  attempted  to  send  currents 
over  wires  too  small  to  carry  them,  they  may  become  so  hot 
as  to  set  fire  to  objects  with  which  they  are  in  contact.  To 
protect  buildings  from  this  danger,  a  fuse  or  strip  of  metal  is 
inserted  in  the  circuit  where  it  enters  the  building.  Before 
enough  current  can  be  sent  over  the  wires  to  overheat  them, 

14 


210  EXPERIMENTAL   GENERAL   SCIENCE 

the  strip  of  metal  melts  and  breaks  the  circuit.  Electric 
flat-irons,  toasters,  and  the  like  are  heated  by  the  resistance 
in  the  small  wires  which  they  contain.  The  mercury  vapor 
lamps  and  lamps  of  similar  structure  give  off  light  from  the 
glowing  vapor  of  mercury,  nitrogen,  or  other  gases. 

176.  Storage  Batteries. — Storage  batteries  are  not  strictly 
places  for  storing  electricity,  but  are  devices  by  means  of  which 
electricity  may  be  obtained  as  wanted.  While  being  charged, 
the  e  lectricity  changes  the  chemical  composition  of  the  con- 
tents of  the  batteries,  and  when  used  as  a  source  of  electricity, 
the  chemicals  gradually  change  back  to  the  original  form,  giv- 
ing up  electric  energy  in  the  process. 

Practical  Exercises 
1.  How  could  you  make  a  weak  electromagnet  stronger? 


2.  What  would  be  the  effect  of  using  steel  instead  of  soft  iron  for  the 
cores  of  electromagnets? 

3.  What  would  be  the  effect  of  connecting  the  wires  of  an  electric 
current  by  means  of  a  glass  rod?     Why? 

4.  Why  could  not  an  alternating  electric  current  be  used  for  electro- 
plating? 

5.  Why  cannot  a  storage  battery  continue  to  take  up  electricity 
indefinitely? 


CHAPTER  XXXI 
LIVING  THINGS 

177.  Organic  and  Inorganic  Bodies. — In  the  early  days  of 
science,  philosophers  regarded  the  universe  as  being  made  up 
of  three  groups  or  kingdoms  containing  the  animals,  the 
plants,  and  the  minerals  respectively.     More  extended  study 
has  shown  that  there  are  really  only  two  kingdoms,  the  living 
or  organic,  containing  all  the  animals  and  plants,  and  the 
non-living  or  inorganic,  containing  the  rocks,  minerals,  air, 
water,  and  the  rest  of  creation.     Living  things  are  composed 
of  the  same  chemical  elements  that  occur  in  other  forms  of 
matter,  but  they  are   sharply  distinguished  from   them  by 
being  organized  into  forms  of  definite  structure  which,  under 
the  influence  of  a  mysterious  force  called  life,  are  capable  of 
feeling,  moving,  growing  or  increasing  in  size,  and  reproducing 
or  increasing  in  numbers.     In  living  things,  also,  each  part 
is  dependent  to  a  certain  extent  on  the  whole  body,  while  in 
the  non-living  no  such  dependence  exists.     When  a  thing  is 
alive,  it  is  continually  adding  new  matter  to  its  substance,  and 
as  constantly  discarding  other  matter  no  longer  of  use.     Only 
living  things  can  do  this;  in  fact,  when  the  adding  process,  or 
assimilation,  and  the  discarding  process,  or  excretion  ceases, 
death  ensues  and  the  body  ultimately  returns  again  to  the 
chemical  elements  from  which  it  was  made. 

178.  Cells. — The  living  parts  of  both  animals  and  plants 
consist  of  a  substance  called  protoplasm  which  is  a  semi-fluid 
much  like  the  white  of  an  egg  in  appearance.     The  smallest 
living  unit  of  protoplasm  is  called  a  protoplast  or  cell.     Such 
cells  are  much  too  small  to  be  seen  with  the  naked  eye,  but 

211 


212 


EXPERIMENTAL  GENERAL   SCIENCE 


they  can  readily  be  seen  with  a  compound  microscope  and 
some  of  the  larger  ones  may  be  distinguished  with  a  good 
lens.  A  typical  cell  consists  of  a  rather  dense  portion,  called 
the  nucleus,  in  which  the  life  processes  center,  and  a  more  fluid 
portion,  the  cytoplasm,  surrounding  it.  In  the  cells  of  plants 
especially,  there  are  one  or  more  cavities,  called  vacuoles,  in 
which  the  cell  sap  is  found.  Plant  cells  are  usually  surrounded 
by  a  thin  membrane  called  a  cell  wall,  which  is  built  up  by 
the  protoplast,  but  animal  cells  seldom  have  these  cell  walls. 


Fia.  79. — Cells  and  their  contents.  A  and  B,  with  red  and  yellow  chromo- 
plasts;  C  with  nucleus  and  green  chloroplasts.  (A,  after  Strasburger;  B,  after 
Frank;  C,  after  Stevens.) 

The  substances  that  cells  build  up  are  sometimes  more  con- 
spicuous than  the  cells  themselves,  especially  in  the  harder 
parts  of  animal  bodies.  The  simplest  animals  and  plants 
consist  of  single  cells  and,  though  so  small,  have  all  the  essen- 
tial capacities  of  living  things.  In  more  complex  forms, 
there  may  be  uncounted  millions  of  cells,  often  varying  greatly 
in  shape.  When  similar  cells  are  arranged  in  groups,  they  are 
called  tissues.  Pith,  wood,  cork,  blood,  muscle,  and  bone  are 
tissues.  The  tissues  are  usually  combined  to  form  organs, 


LIVING   THINGS  213 

such  as  the  stomachs  of  animals  or  the  leaves  of  trees.  It  is 
the  occurrence  of  these  organs  in  all  forms  of  life  except  the 
very  lowest  that  causes  us  to  name  the  group  to  which  they 
belong  the  organic  kingdom. 

179.  Growth. — In  a  sense,  crystals  may  be  said  to  grow  in 
that  they  increase  in  size,  but  this  increase  is  always  from 
without   by   the   addition   of  similar  molecules.     All  living 
things  grow  by  the  addition  of  matter  taken  into  their  bodies 
and  there  built  up  into  new  molecules.     In  living  things  also 
there  is  a  regular  cycle  of  development.     Beginning  with  a 
single  cell,  the  organism  increases  in  size  by  the  repeated 
division  of  its  cells  until  it  reaches  a  determinate  size  and 
becomes  mature.     It  then  reproduces,  or  gives  rise  to  new 
individuals,  for  a  certain  time,  and  finally  declines  to  old 
age  and  ceases  to  exist.     Of  the  two  groups,  the  animals  are 
more  closely  circumscribed  both  as  regards  length  of  life  and 
size,  but  though  some  plants  may  continue  to  live  for  several 
centuries,  there  are  certain  limits  as  to  their  size  beyond  which 
they  rarely  pass.     Animals  again,  usually  have  very  definite 
shapes,  though  the  simplest  of  them  as  well  as  the  simplest 
plants  are  not  thus  restricted.     Though  the  plant  body,  as  a 
whole,  has  not  as  definite  a  form  as  has  the  animal  body, 
some  organs,  such  as  flowers,  fruits  and  seeds,  are  constant  in 
this  respect. 

180.  Food  Making. — The  material  which  living  things  build 
into  their  bodies  and  from  which  they  obtain  their  necessary 
energy  is  called  food.     The  food  materials  are  the  chemical 
elements  in  the  soil  and  air,  and  plants  are  the  only  organisms 
in  nature  that  can  combine  them  into  foods.     In  consequence, 
the  entire  animal  world  is  dependent  upon  plants  for   its 
existence.     The  energy  in  food  making  is  derived  from  sun- 
light by  the  green  parts  of  plants.    In  these  parts,  the  cells 
contain  small  green  bodies  called  chloroplasts    which    stop 
some  of  the  rays  of  light  and  change  them  into  an  available 


214 


EXPERIMENTAL  GENERAL  SCIENCE 


form  of  energy.  In  the  formation  of  ordinary  foods,  the 
plant  uses  the  water  from  the  soil  and  the  carbon  dioxide  of 
the  air.  All  the  carbon  found  in  plants  is  obtained  in  this  way 
from  carbon  dioxide.  Since  only  the  carbon  is  used  in  food 
making,  the  oxygen  is  given  off  again  by  the  plant.  The 
process  of  making  food  in  this  way  is  known  as  photosynthesis. 
There  are  three  classes  of  foods  commonly  formed  by  plants, 
namely,  carbohydrates,  fats  or  oils,  and  proteins.  The  car- 
bohydrates are  most  common  and  are  represented  by  such 


r 


FIG.  80.  —  Sectional  and  surface  view  of  part  of  moss  leaf  showing  chloro- 
plasts.     (Stevens.) 


substances  as  starch  (CeHioOs),  grape  sugar  (CeH^Oe),  cane 
sugar  (Ci2H22On),  and  cellulose  (CeHioOs).  In  carbohy- 
drates, the  hydrogen  present  is  always  twice  the  amount  of 
the  oxygen.  Most  of  the  oils  with  which  we  are  familiar  are 
also  produced  by  plants.  These  contain  carbon,  hydrogen, 
and  oxygen,  but  the  oxygen  is  usually  in  smaller  proportions 
than  in  the  carbohydrates.  Proteins  contain  the  three  chem- 
ical elements  found  in  other  foods  with  the  element  nitrogen 
added.  Protoplasm,  lean  meat,  and  albumen  are  examples 
of  proteins.  The  bodies  of  all  animals  and  plants,  though 


LIVING   THINGS  215 

made  of  the  same  materials,  differ  considerably  in  composi- 
tion. The  animals  have  characteristically  nitrogenous  tissues, 
and  the  plants  carbonaceous  tissues. 

181.  Digestion. — The  food  stores  of  plants  are  usually  in 
insoluble  form,  and  have  to  be  made  soluble,  or  digested,  before 
they  can  be  built  up  into  living  tissues.     Digestion  is  accom- 
plished by  the  aid  of  certain  ferments  called  enzymes,  and  re- 
quires the  presence  of  a  certain  amount  of  water  for  their 
activities.     The  process  is  comparatively  simple  in  plants,  but 
in  all  but  the  simplest  animals  there  are  special  organs  for 
containing  the  food  during  the  digestive  process  and  various 
glands  for  secreting  the  enzymes  and  other  digestive  fluids 
needed.     The  digested  food  is  carried  in  solution  to  the  point 
in  the  body  where  it  is  used.     In  plants,  the  solution  is  com- 
monly called  sap;  in  animals,  it  is  the  blood. 

182.  Respiration. — One  of  our  commonest  sources  of  energy 
is  the  union  of  oxygen  with  carbon.     In  living  things  this  is 
practically  the  only  source  of  energy.     Both  animals  and 
plants  respire,  taking  in  oxygen  for  the  purpose,  and  giving 
out  carbon  dioxide.     The  real  respiration  occurs  in  the  cells, 
but  in  animals  there  are  usually  organs  for  rapidly  carrying 
oxygen  to  them.     Plants,  being  less  active  than  animals,  re- 
spire more  slowly,  but  the  process  is  the  same  in  all.     From 
the  fact  that  in  photosynthesis  plants  take  up  carbon  and  give 
off  oxygen,  it  is  often  assumed  that  the  process  of  respiration 
or  breathing  in  plants  is  exactly  the  opposite  of  that  in  animals, 
but  this  is  a  mistake.     Plants  respire  like  animals,  but  have 
in  addition,  the  capacity  for  photosynthesis  in  which  they 
take  in  carbon  dioxide  and  give  off  oxygen.     It  is  interesting 
to  note  that  the  formation  and  use  of  food  is  somewhat  analo- 
gous to  what  goes  on  in  the  storage  battery  in  that  the  energy 
from  the  sun,  like  the  electric  current,  is  made  to  produce 
certain  changes  in  matter,  and  this  energy  is  obtained  again 
when  the  changes  in  matter  are  reversed. 


216 


EXPERIMENTAL  GENERAL  SCIENCE 


183.  Reproduction. — All  living  things  must  reproduce  them- 
selves, else  their  particular  forms  would  soon  cease  to  exist. 
In  the  simplest  kinds,  reproduction  consists  in  the  dividing 
of  the  cell  into  two  equal  parts  each  of  which  grows  up  and 
becomes  a  new  individual.  In  higher  forms,  reproduction  is 
a  function  of  certain  cells  set  apart  for  the  purpose.  These 
may  divide  into  a  number  of  small  bits  called  spores,  each  of 
which  is  capable  of  producing  a  new  individual,  or  they  may 
form  similar  bodies  which  are  unable  to  produce  new  indi- 
viduals without  uniting  in  pairs.  Such  uniting  bodies  are 
called  gametes.  In  all  the  higher 
animals  and  plants,  reproduction  is 
by  the  union  of  gametes.  When  the 
uniting  gametes  differ  in  size,  as  they 
do  in  the  higher  kinds,  the  smaller  one 
is  called  the  sperm  and  the  larger  one 
the  egg.  Two  sperms,  however,  can- 
not form  a  new  organism,  nor  can  two 
eggs.  The  union  of  a  sperm  and  an 
egg  is  essential  to  the  production  of  a 
new  being  in  this  way.  With  a  differ- 

FIG.     81. — Cell     division 

and  the  formation  of  a  ence  in  the  size  of  the  gametes,  it  be- 
colony 'in  green  stain  (Pleuro-  Comes  possible  to  indicate  their  sex. 

coccus).     (Gager.) 

The  sperm  is  always  called  male,  and 

the  egg  female.  In  most  plants,  and  in  the  simpler  animals,  a 
single  individual  may  produce  both  sperms  and  eggs,  but  in  the 
higher  animals  each  kind  of  gamete  is  produced  by  a  separate 
individual  which  is  therefore  called  male  or  female  as  the  case 
may  be.  In  plants,  the  organs  of  reproduction  are  found  in 
a  complicated  structure  called  the  flower.  The  eggs  are  pro- 
duced in  one  or  more  bottle-shaped  organs  called  carpels,  occu- 
pying the  center  of  the  flower,  and  the  sperms  originate  in 
certain  cells,  called  pollen  grains,  produced  by  the  pin-shaped 
organs  or  stamens  surrounding  the  carpels.  The  transfer  of 


LIVING   THINGS 


217 


the  pollen  grains  to  the  receptive  parts  of  the  carpels  is 
called  pollination.  The  colored  parts  of  flowers,  known  as 
sepals  and  petals,  protect  the  other  organs  and  assist  in  the 
work  of  pollination  by  attracting  bees  and  other  insects 
which,  in  their  efforts  to  get  at  the  nectar,  are  forced  to 


itil 


FIG.  82. — Semi-diagrammatic  representation  of  nuclear  division  which  occurs 
whenever  a  cell  divides.     (Stevens.) 

brush  against  the  stamens  and  so  become  dusted  with  pollen 
to  be  carried  to  other  flowers.  Flowers  which  lack  petals 
and  sepals  are  usually  pollinated  by  the  wind.  In  some 
species  of  plants,  the  stamens  are  borne  on  one  plant  and 
the  carpels  on  another,  Such  species  are  said  to  be  dioecious. 


218 


EXPERIMENTAL  GENERAL  SCIENCE 


When  the  stamens  are  borne  on  different  parts  of  the  same 
plant  the  species  are  moncecious.  Most  plants,  however, 
have  stamens  and  carpels  in  the  same  flower. 

184.  Species  and  Higher  Groups. — The  most  careless  ob- 
server must  have  noticed  that  the  differences  that  separate  one 
living  thing  from  another  are  not  always  of  the  same  magni- 
tude. There  is  a  greater  difference  between  a  cow  and  a 
cabbage  than  there  is  between  a  turnip  and  a  cabbage,  or  be- 
tween a  cow  and  a  sheep.  If  we  continue  to  narrow  our  com- 
parisons, we  soon  come  to  groups  in  which  the  individuals 


FIG.  83. — A  typical  flower  with  all 
of  the  floral  organs. 


Q  \> 

FIG.  84. — Compound  carpels. 


resemble  one  another  more  than  they  resemble  anything  else. 
Such  a  group  is  called  a  species.  All  garden  sunflowers,  or 
white  clovers,  or  English  sparrows,  belong  to  a  single  species. 
We  are  well  aware,  however,  that  there  are  other  kinds  of 
sunflowers,  clovers,  and  sparrows  which  resemble  our  typical 
species  more  than  they  do  other  plants  or  animals.  It  is, 
therefore,  possible  to  arrange  species  which  resemble  one 
another  into  larger  groups  called  genera  (singular  genus}.  In 
the  same  way  we  may  assemble  the  genera  into  families  and 
the  families  into  orders.  For  instance,  there  are  a  number  of 


LIVING  THINGS  219 

different  species  in  the  rose  genus  (Rosa),  but  they  do  not 
differ  enough  to  be  placed  in  different  genera.  When  we  ex- 
amine the  strawberry  (Fragaria),  the  blackberry  (Rubus),  the 
bridal  wreath  (Spiraea),  and  a  large  number  of  others,  we  find 
the  flowers  are  all  of  the  typical  rose  pattern,  but  they  differ 
enough  to  make  it  necessary  to  place  them  in  different  genera. 
We  group  all  these  genera  in  the  rose  family  (Rosacece),  and 
this  great  family,  with  several  other  related  ones  forms  the 
rose  order  (Resales).  A  similar  grouping  is  found  in  animals. 
Many  such  groups  in  both  the  animal  and  plant  worlds  are 
recognized  almost  at  sight  as  cats,  dogs,  deer,  whales,  mice, 
bats,  bees,  asters,  pines,  lilies,  grapes,  and  the  like. 

186.  Scientific  Names. — Each  species  of  animal  or  plant 
has  its  own  name  consisting  of  two  words  similar  in  significance 
to  our  own  names.  One  of  these  words  is  the  individual  or 
specific  name,  such  as  our  so-called  " given "  or  Christian  name; 
the  other  is  the  group  name  which  it  shares  with  all  the  indi- 
viduals in  the  genus,  just  as  we  share  our  family  name  with 
brothers  and  sisters.  In  reference  lists,  our  family  or  generic 
names  are  always  written  first,  and  the  same  is  true  of  plants 
and  animals.  When  we  mention  these  latter,  however,  we 
always  speak  the  generic  name  first.  Thus  in  Trifolium  repens, 
the  name  of  the  white  clover,  Trifolium  is  the  generic  name 
and  repens  the  specific  one.  The  red  clover  is  Trifolium 
pratense,  the  yellow  clover,  Trifolium  agrarium,  and  so  on. 
In  addition  to  these,  most  species  have  one  or  more  common 
or  vernacular  names.  The  question  is  often  asked  why  one 
should  use  the  scientific  names  when  the  common  names  are 
usually  so  much  easier  to  pronounce,  and  the  answer  is  that 
since  the  same  species  of  plants  and  animals  are  often  found 
in  different  countries,  great  confusion  would  ensue  if  the 
natives  of  each  country  used  only  the  name  current  for  it  in 
his  own  tongue.  The  scientific  names,  derived  mostly  from 
the  ancient  Latin  and  Greek,  are  fixed  in  their  meanings,  and 


220  EXPERIMENTAL   GENERAL   SCIENCE 

by  using  them  one  may  be  understood  wherever  scientific  men 
are  found. 

186.  Distribution. — Evidences  of  organic  life  are  everywhere 
present  on  the  earth.  -The  shallow  waters  teem  with  aquatic 
animals  and  plants,  other  forms  creep  or  walk  on  the  soil,  or 
burrow  into  it,  while  still  others  are  rooted  in  the  soil.  Other 
forms  float  in  the  air  or  move  through  it  by  their  own  efforts. 
The  simplest  living  things  are  most  widely  distributed.  They 
swarm  in  all  soils  and  are  to  be  found  on  mountain  tops,  in 
the  arctic  regions,  and  in  the  oceans  depths.  Inorganic  sub- 
stances on  the  globe  are  usually  distributed  in  a  haphazard 
way,  but  the  distribution  of  living  things  depends  so  much  on 
temperature,  pressure,  moisture,  and  light,  that  there  are 
usually  pretty  definite  limits  to  the  range  of  each  species. 
Oceans,  deserts,  mountain  ranges,  and  extensive  forests, 
frequently  act  as  barriers  to  the  spreading  of  a  species  in  cer- 
tain directions,  and  for  this  reason  the  plants  or  animals  of 
distant  lands  are  seldom  identical,  though  the  flora  (plants) 
and  fauna  (animals)  of  the  two  regions  may  contain  many 
related  species.  Living  things  are  more  or  less  adapted  to  the 
places  in  which  they  live,  and  cannot  survive  as  well  in  any 
other,  owing  to  the  differences  in  temperature  elevation  and 
the  like.  A  few  may  be  adapted  to  other  regions  by  making 
new  adjustments  to  their  surroundings.  This  is  known  as 
acclimatization.  The  flora  and  fauna  change  more  rapidly  as 
one  travels  north  and  south  than  they  do  if  we  travel  east  and 
west.  The  higher  plants  are  unable  to  move  about  by  their 
own  efforts,  as  animals  do,  but  the  young  plants  in  the  seeds 
are  usually  provided  with  some  means  of  locomotion  by 
which  they  spread  into  new  regions.  Many  seeds  have  tufts 
of  hairs  which  serve  as  parachutes  delaying  their  fall  to  the 
ground  and  thus  carrying  them  to  new  places,  others  have 
winglike  projections  and  are  blown  about  by  the  wind,  and 
still  others  are  covered  with  a  juicy  pulp  which  ensures  their 
being  carried  to  new  localities  by  birds  and  other  animals. 


LIVING   THINGS  221 

187.  Plant  and  Animal  Forms. — While  plants  are  less  fixed 
as  to  form  than  animals,  there  are  certain  groups  into  which 
they  are  naturally  divided  on  account  of  their  structure  or 
length  of  life.  It  is  customary  to  group  plants  as  annuals, 
which  live  but  a  single  season,  and  perennials  which  may  live 
for  many  seasons.  The  perennials  are  further  divided  into 
the  herbaceous  species  which  die  down  to  the  ground  at  the 
approach  of  cold  or  dry  seasons,  and  the  woody  species  which 
do  not.  The  latter  are  further  divided  into  the  trees  with  a 
single  woody  stem,  shrubs  with  several  stems,  and  the  lianes 
or  vines  whose  stems,  though  woody,  are  much  too  weak  to  hold 
themselves  erect  and  therefore  climb  on  other  plants.  The 
animals,  instead  of  being  grouped  according  to  length  of  life, 
as  are  the  plants,  are  more  frequently  grouped  into  Verte- 
brates in  which  there  is  a  spinal  column,  and  Invertebrates  in 
which  this  is  lacking.  The  vertebrates  contain  the  highest 
types  such  as  the  fish,  amphibians  (frogs,  etc.),  reptiks,  birds, 
and  mammals,  but  are  greatly  outnumbered  by  the  inverte- 
brates. The  vertebrates  never  have  more  than  four  append- 
ages for  locomotion,  and  the  highest  division  of  them,  the 
mammals,  nourish  their  young  with  milk.  The  most  note- 
worthy groups  of  invertebrates  are  the  Mollusca,  containing 
the  snails,  clams,  oysters,  and  other  " shell  fish,"  and  the 
Arthropoda  which  include  the  crabs,  lobsters,  spiders,  and 
insects.  All  in  this  latter  group  have  more  or  less  distinctly 
jointed  bodies,  and  from  six  to  ten  or  more  appendages  for 
locomotion. 

Practical  Exercises 

1.  Strip  a  piece  of  fresh  epidermis  from  an  onion  bulb,  mount  in  a  drop 
of  water  on  a  slip  of  glass  and  examine  with  a  simple  lens.     The  cells  may 
be  easily  seen.     (If  a  compound  microscope  is  available,  it  will  show  the 
cell  wall,  cytoplasm  and  nucleus.) 

2.  Mount  any  of  the  green  growths  (algse)  found  floating  in  ponds  as 
directed  in  exercise  1  and  examine.     Note  the  colored  bodies  which 
function  in  food  making. 


222  EXPERIMENTAL  GENERAL  SCIENCE 

8.  Name  as  many  species  of  oaks  as  you  can. 

4.  Examine  various  kinds  of  flowers  or  consult  the  pictures  in  books 
and  name  all  the  members  of  the  Leguminosse  (pea  family)  with  which 
you  are  familiar. 

6.  The  trailing  arbutus  (Epigaea)  is  called  mayflower,  ground  laurel 
and  ground  ivy.  What  vernacular  name  do  you  use  for  it? 

6.  Which  of  the  following  names  do  you  use  for  Azalea  nudiflora: 
pinkster,  azalea,  mayflower,  honeysuckle. 

7.  Following  is  a  list  of  generic  names.     Make  a  list  of  those  with 
which  you  are  familiar.     Are  they  the  names  of  plants  or  animals? 
Cosmos,    Canna,   Salvia,   Zinnia,    Magnolia,   Chrysanthemum,   Oxalis, 
Clematis,  Iris,  Phlox,  Geranium,  Viola,  Lilium. 

8.  Visit  a  piece  of  dry  ground  and  a  swamp.     Are  the  plants  alike  on 
both  places?    Why? 

9.  Name  an  annual,  an  herbaceous  perennial,  a  shrub,  a  tree  and  a 
liane  with  which  you  are  familiar. 

10.  Make  a  list  of  ten  invertebrates  with  which  you  are  familiar. 

11.  Name  the  nearest  barrier  to  the  spread  of  plants  in  your  region. 

12.  Does  the  barrier  mentioned  in  the  preceding  exercise  act  equally 
well  as  a  barrier  to  animals? 

13.  Name  a  plant  with  which  you  are  familiar  whose  distribution  in 
your  region  is  limited  by  moisture. 

14.  Which  seem  able  to  grow  best  in  a  variety  of  situations,  the  weeds 
or  the  other  wildflowers? 

15.  Examine  various  flowers  and  identify  stamens  and  carpels.    Which 
should  be  called  male  organs? 


CHAPTER  XXXII 
EVOLUTION 

188.  Origin  of  Living  Things. — From  the  earliest  times,  the 
great  diversity  of  animal  and  plant  life  on  the  earth  has 
attracted  the  attention  of  scientists  and  philosophers,  and 
given  rise  to  much  speculation  regarding  the  origin  and  sub- 
sequent development  of  the  various  forms.  It  was  once 
thought  that  all  forms  of  life  were  the  objects  of  special  crea- 
tion, and  that  they  appeared  upon  the  earth  at  one  time  and 
in  substantially  the  forms  in  which  we  now  find  them.  Strong 
objections  to  this  theory  have  arisen  since  exploration  of  the 
earth's  crust  has  discovered  the  fossil  remains  of  many  forms 
quite  unlike  those  of  the  present.  These  remains  are  not  only 
found  in  the  soil,  but  occur  embedded  in  the  solid  rocks,  show- 
ing that  they  must  have  existed  even  before  some  of  the  rocks 
were  formed.  These  extinct  animals  and  plants,  though 
very  different  from  present  forms,  bear  certain  well-defined 
resemblances  to  them,  and  the  suggestion  has  often  been  made 
that  some  sort  of  relationship  must  connect  them.  The  doc- 
trine of  special  creation,  however,  dominated  scientific  thought 
almost  universally  until  the  last  century,  when  an  Englishman, 
Charles  Darwin,  wrote  an  epoch-making  book  on  the  "  Origin 
of  Species"  which  almost  completely  changed  this  view.  In 
this  book  Darwin  set  forth  with  much  skill  a  great  deal  of 
evidence  to  prove  that  the  living  things  now  on  the  earth 
have  descended  from  these  earlier  arid  less  highly  specialized 
organisms  through  gradual  changes  during  immense  periods 
of  time.  Since  the  announcement  of  the  Darwinian  Theory, 
the  accumulation  of  much  additional  evidence  has  only 

223 


224  EXPERIMENTAL   GENERAL   SCIENCE 

served  to  strengthen  the  general  proposition,  though  different 
phases  of  the  subject  have  been  modified  in  some  respects 
as  more  facts  have  been  discovered.  It  is  still  a  question  where 
the  first  life  on  the  earth  came  from,  but  the  idea  that  living 
things  began  as  simple  cells  and  that  all  the  animals  and 
plants  have  arisen  from  them  by  a  succession  of  changes  or 
adaptations  is  now  commonly  accepted.  This  latter  concep- 
tion of  the  origin  of  living  things  is  known  as  evolution,  and 
is  strongly  opposed  to  the  theory  of  special  creation. 

189.  Change  in  Nature. — Change  is  one  of  the  most  notice- 
able characteristics  of  nature.  The  seasons  wax  and  wane, 
sunshine  succeeds  storm,  day  alternates  with  night,  plants 
spring  up  and  die,  and  even  the  solid  earth  itself  is  slowly 
changing  through  the  ceaseless  action  of  a  variety  of  agencies. 
After  a  thunderstorm,  every  ditch  and  stream  will  be  found 
carrying  a  heavy  load  of  mud  taken  from  the  surface  of  the 
soil.  It  is  very  apparent,  therefore,  that  the  storms  of  a 
single  year  must  have  an  appreciable  effect  in  wearing  down 
the  elevations,  and,  if  given  sufficient  time,  this  single  agency 
might  reduce  the  earth  to  a  nearly  level  plain.  There  are, 
however,  many  other  agencies  aiding  in  the  work.  The  oxygen 
of  the  air  combines  with  various  elements  in  the  rocks  and 
causes  their  decay.  Carbon  dioxide  acts  in  the  same  way. 
Water,  especially  when  containing  acids  from  decaying  vege- 
tation, dissolves  out  the  minerals,  and  running  water  contain- 
ing sediment  wears  down  the  mountain  valleys  appreciably. 
Alternating  heat  and  cold  breaks  up  the  rocks,  water  percolates 
into  tiny  crevices  and  freezing  expands  and  widens  them. 
The  roots  of  plants  add  their  mite  toward  turning  the  rocks 
into  soil,  and  earthquakes  and  volcanos  rend  and  change  the 
solid  rocks  themselves.  That  the  particles  of  the  soil  are 
really  carried  away  is  shown  by  the  formation  of  mud  banks  or 
deltas  at  the  mouths  of  great  rivers,  by  the  islands  built  up 
here  and  there  in  the  streams,  by  filled  lakes  and  river  terraces, 


EVOLUTION  225 

and  by  the  mud-covered  ocean  floor.  The  present  appear- 
ance of  the  earth  is  only  one  stage  in  a  long  succession  of 
changes;  indeed,  it  is  believed  that  the  earth  was  once  a 
body  much  hotter  than  the  sun — a  mass  of  incandescent 
gases  in  fact — and  that  it  has  reached  its  present  shape 
through  a  cooling  and  shrinking  process  extending  over  such 
vast  stretches  of  time  that  a  million  years  is  but  a  unit  of 
measurement. 

190.  Organic  Evolution. — It  is  very  evident  that  the  first 
plants  and  animals  did  not  appear  on  the  earth  until  some  parts 
of  it  at  least  had  cooled  sufficiently  to  assume  the  solid  state 
with  a  temperature  not  much  higher  than  is  found  at  the 
equator   at   present.     That   the   earth  had  not  reached  its 
present  form  when  such  organisms  appeared  is  shown  by  the 
fact  that  we  find  the  remains  of  both  animals  and  plants  in 
all  but  the  oldest  rocks.     Coal,  as  everybody  knows,  is  com- 
posed of  plant  remains,  and  yet  it  is  found  everywhere  deep 
in  the  earth   where  no   plants   could  grow.     Nearly  every 
museum  has  a  collection  of  fossil  plants  and  animals  taken  from 
the  rocks.     The  great  changes  in  the  earth  which  have  un- 
doubtedly taken  place  since  the  coal  beds  were  formed  must 
have  sufficed  to  exterminate  an  immense  number  of  species, 
genera,  or  even  larger  groups,  but  in  the  process  making  new 
habitats  in  which  other   races  of  animals  and  plants  could 
exist. 

191.  Variation  in  Nature. — If  we  assume  that  the  animals 
and  plants  of  today  have  descended  from  earlier  and  less 
complex  species  by  gradual  changes  in  their  form  and  struc- 
ture, we  shall  find  it  necessary  to  show  that  living  things  are 
capable  of  making  such  changes.     This,  however,  is  not  a 
difficult  matter.     No  two  objects  in  nature  are  exactly  alike. 
Whether  we  are  gathering  flowers,  choosing  an  apple,  or  select- 
ing a  kitten  or  puppy  from  among  its  brothers  and  sisters, 
there  is  always  room  for  a  choice  because  of  the  small  dif- 

15 


226  EXPERIMENTAL  GENERAL  SCIENCE 

ferences  they  present.  This  tendency  toward  variation  which 
all  organic  life  seems  to  possess  makes  it  possible  for  some 
groups  to  outstrip  others  in  the  race  for  life.  We  can  readily 
understand  that  in  case  a  given  species  or  race  of  animals  or 
plants  finds  itself  in  surroundings  where  the  conditions  of 
life  are  growing  increasingly  difficult,  the  group  whose  varia- 
tions are  most  favorable  to  their  success  is  the  group  likely 
in  the  long  run  to  survive.  When  an  area  becomes  over- 
populated,  for  instance,  the  race  with  the  ability  to  quickly 
move  into  new  regions  and  adjust  itself  to  the  conditions  there, 
might  not  only  survive,  but  originate  new  lines  of  descent. 

192.  The  Struggle  for  Existence. — The  fact  which  makes 
variation  in  animals  and  plants  of  much  importance  is  the 
tendency  which  every  species  has  to  produce  more  young 
than  can  possibly  come  to  maturity.  A  single  fern  leaf  may 
produce  several  million  spores  in  a  season,  and  the  plant  may 
have  several  such  leaves,  while  a  single  locality  may  contain 
thousands  of  fern  plants.  If  every  spore  should  grow  into  a 
new  fern  with  spores  of  its  own,  and  so  on,  it  would  only  be  a 
few  years  before  there  would  be  enough  of  this  single  species 
to  thickly  populate  every  square  foot  of  the  earth's  surface. 
Such  a  thing  is  not  likely  to  occur,  however,  because  every 
other  form  of  life  is  similarly  attempting  to  conquer  the  world 
for  itself.  This  can  only  result  in  a  vigorous  struggle  for 
existence  in  which  the  strongest  and  best  fitted  to  survive 
are  practically  the  only  ones  that  do  so.  In  such  a  struggle, 
however,  a  fortunate  variation  may  save  a  form  from  extinc- 
tion by  enabling  it  to  overcome  the  forces  opposed  to  it. 
When  this  phase  of  the  subject  is  brought  to  his  attention,  the 
most  casual  observer  will  be  able  to  recall  evidences  of  such  a 
struggle.  Animals,  as  we  know,  constantly  feed  on  plants, 
but  the  plants  even  up  matters  to  some  extent  by  feeding  on 
animals,  for  the  diseases  that  afflict  animals,  including  man, 
are  nearly  all  of  plant  origin.  Plants  struggle  with  plants, 


EVOLUTION  227 

and  animals  with  animals,  for  food,  and  the  more  nearly  related 
they  happen  to  be,  the  fiercer  the  struggle,  since  the  require- 
ments of  closely  related  species  are  very  similar.  There  are 
also  the  effects  of  weather  and  climate  to  be  considered. 
Frost,  cold,  and  drought  cause  the  death  of  many  species 
annually.  Many  other  circumstances  have  a  bearing  on  the 
struggle,  but  in  the  end  those  forms  best  fitted  to  survive 
remain  to  reproduce  their  race,  while  others  disappear.  Thus 
the  forms  on  the  earth  are  the  results  of  what  might  be  called 
a  natural  selection  in  which  the  unfit  are  slowly  weeded  out 
and  only  the  best  preserved.  If  an  organism  happens  to  find 
itself  in  surroundings  favorable  to  its  development,  its  rapid 
increase  in  numbers  is  convincing  testimony  of  the  struggle  it 
is  under  elsewhere.  All  the  English  sparrows  in  America  are 
the  progeny  of  a  few  pairs  of  birds  brought  to  this  country  less 
than  fifty  years  ago.  Rabbits  taken  to  Australia  have  over- 
run that  country  in  a  similar  way.  The  prickly  lettuce  and 
Russian  thistle  have  spread  over  the  United  States  in  the  past 
half  century.  Many  similar  instances  could  be  mentioned. 

193.  The  Mutation  Theory. — In  recent  years  a  Dutch 
botanist,  Hugo  DeVries,  has  suggested  certain  modifications 
of  the  Darwinian  Theory  based  on  a  large  amount  of  experi- 
mental evidence.  These  modifications  are  embodied  in  what 
is  known  as  the  Mutation  Theory.  The  essential  difference 
between  the  Darwinian  Theory  and  the  Mutation  Theory  is 
that  the  first  assumes  a  gradual  change  from  one  species  to 
another,  while  the  second  asserts  that  variation  is  not  contin- 
uous but  occurs  by  sudden  leaps,  as  it  were.  One  of  the  chief 
objections  to  the  Darwinian  Theory  was  that  the  " missing 
links"  supposed  to  connect  one  species  with  another  could 
never  be  found.  The  Mutation  Theory  accounts  for  the 
absence  of  such  connecting  links  by  the  statement  that  they 
never  existed,  and  that  each  new  form  springs  practically 
complete  from  some  nearly  related  one.  This  theory  best 


228  EXPERIMENTAL   GENERAL  SCIENCE 

accounts  for  the  appearance  of  a  large  number  of  sports  such  as 
white  flowers  among  red-flowered  plants,  yellow  fruits  on 
plants  that  normally  have  red  ones,  and  an  immense  number  of 
other  variations  of  this  kind.  If  the  different  connecting 
links  assumed  by  the  Darwinian  Theory  really  did  exist,  we 
should  be  unable  to  distinguish  either  species  or  genera.  But 
while  it  is  becoming  increasingly  apparent  that  the  Mutation 
Theory  will  explain  most  of  the  puzzles  connected  with  the 
origin  of  animals  and  plants,  there  is  still  a  possibility  that  a 
goodly  number  of  forms  may  have  arisen  by  gradual  change,  as 
suggested  by  the  Darwinian  Theory,  especially  in  those  groups 
most  closely  linked  together. 

194.  Elementary    Species. — The    older   naturalists,    while 
admitting  the  origin  of  living  things  through  evolution,  re- 
garded the  species  once  formed  as  something  fixed  and  unvary- 
ing, but  the  Mutation  Theory  has  shown  that  such  species  are 
probably  a  composite  of  a  number  of  less  conspicuous  forms 
which  are  known  as  elementary  species.     These  are  what  we 
commonly    call   varieties.     Several    plants    are   known    that 
rather  constantly  produce  such  elementary  species  or  "mu- 
tants," and  it  is  probable  that  other  species  may  be  made  to  do 
so.     When  a  mutant  is  produced  that  is  better  adapted  to  its 
surroundings  than  the  species  from  which  it  came,  it  may  ulti- 
mately supplant  the  parent  form  in  the  locality;  otherwise  it  is 
soon  swamped  by  the  multitudes  of  the  ordinary  form.     If 
protected  from  extinction  by  cultivation,  it  may  prove  to  be 
much  superior  to  the  original  form.     The  different  varieties  of 
apples  may  be  regarded  as  elementary  species.     All  apples 
belong  to  a  single  species  of  apple,  yet  each  possesses  character- 
istics of  its  own  which  make  it  easily  recognized  by  the 
student. 

195.  Plant  and  Animal  Breeding. — Nearly  all  the  plants 
used  by  man  are  superior  to  the  plants  of  the  same  species 
found  in  the  wild  condition.     In  some  cases  our  improved 


EVOLUTION  229 

varieties  are  so  different  from  the  original  forms  that  the  two 
are  scarcely  recognized  as  belonging  to  the  same  species.  For 
instance,  the  prickly  lettuce,  a  common  weed  of  waste  ground, 
is  the  parent  of  the  garden  lettuce.  The  same  condition  exists 
with  regard  to  the  animals,  though  plants,  being  less  highly 
organized  and  yielding  more  readily  to  experiment,  probably 
show  the  most  remarkable  results.  In  producing  these 
forms  man  has  followed  nature's  methods  in  selecting  those 
most  suited  to  his  purpose.  What  man  considers  best,  how- 
ever, may  not  be  the  best  from  nature's  standpoint,  and  are 
possibly  not  fitted  to  survive  in  a  struggle  with  their  environ- 
ment, but  under  man's  protection  this  is  no  obstacle  to  con- 
tinued existence.  A  large  number  of  our  cultivated  plants 
must  be  protected  from  the  weeds  by  cultivation.  Domestic 
animals  must  be  protected  in  like  manner  from  their  foes. 
Selection,  however,  is  only  one  phase  of  breeding.  In  plants 
especially,  hybridizing  or  the  union  of  the  sperms  and1  eggs  of 
different  species  or  varieties,  is  frequently  utilized.  Sports  of 
all  kinds  are  of  value  in  affording  a  point  from  which  to  begin 
experiments.  In  order  to  induce  a  species  to  sport,  variations 
of  the  food,  temperature,  and  other  characteristics  of  the 
surroundings  are  often  made.  In  the  early  history  of  breeding 
the  forms  to  be  propagated  were  selected  more  or  less  arbitrar- 
ily, but  with  the  discovery  of  Mendel's  Law  of  inheritance,  the 
work  of  breeding  now  proceeds  upon  more  scientific  lines. 
Mendel's  discovery  consists  essentially  in  the  recognition  of 
the  fact  that  the  gametes — eggs  and  sperms — of  a  pure  organ- 
ism carry  only  the  characteristics  of  that  organism,  and  when 
the  gametes  of  two  different  forms  are  united,  these  characters 
may  be  rearranged  in  new  combinations  with  great  accuracy. 
With  these  facts  clearly  understood,  it  becomes  possible,  by 
crossing  plants  or  animals  in  different  ways,  to  obtain  rapid 
improvement  in  the  species  selected  and  thus  produce  many 
new  and  promising  forms. 


230  EXPERIMENTAL  GENERAL   SCIENCE 

Practical  Exercises. 

1.  Make  a  list  of  the  fossil  animals  and  plants  that  you  have  seen. 

2.  If  there  are  any  fossils  in  the  rocks  of  your  region,  describe  them. 


3.  Are  the  specimens  mentioned  in  exercise  2  of  animal  or  vegetable 
origin? 


4.  Name  a  place  in  your  region  that  is  being  built  up  by  the  action  of 
water. 


5.  Name  a  place  in  your  region  that  is  being  torn  down  by  water. 


6.  After  the  next  rain  find  places  in  the  nearest  field  to  illustrate  the 
actions  mentioned  in  exercises  4  and  5. 


7.  Try  to  find  two  leaves  exactly  alike. 


8.  Examine  mulberry  and  sassafras  trees  or  Boston  ivy  for  leaves  of 
different  shape.     How  do  these  differ? 


9.  Which  can  move  into  a  new  region  quickest,  a  sparrow,  a  toad  or  a 
squirrel? 


10.  Which  can  move  into  a  new  region  quickest,  dandelions,  burdocks 
or  hickory  trees? 

11.  Examine  any  open  weedy  place  for  examples  of  a  struggle  for 
existence.     Is  the  struggle  for  water,  light,  food  or  sufficient  room? 


12.  Examine  the  nearest  flowery  field  for  examples  of  variation.     In 
what  does  the  variation  consist,  color,  size,  shape  or  number  of  parts? 


CHAPTER  XXXIII 
BACTERIA 

196.  Nature  of  Bacteria. — Bacteria,  often  called  germs,  are 
the  smallest  of  living  things.     They  can  be  seen  only  with  the 
highest  powers  of  the  compound  microscope  and  some  are  so 
small  that  fifty  thousand  in  single  file  would  not  make  a  line 
more  than  an  inch  long.     Bacteria  are  really  plants,  their 
nearest  relations  being  the  seaweeds,  mushrooms,  puffballs, 
and  yeasts,  but  they  are  much  smaller  than  any  of  these. 
Each  consists  of  a  single  cell,  the  shape  of  which  varies  with 
the  species.     All,  however,  resemble  certain  types  enough  to 
enable  us  to  classify  them  as  round,  rod-shaped,  and  twisted 
or  corkscrew-like  forms.     Bacteria  occur  almost  everywhere; 
in  the  air  we  breathe,  in  the  water  we  drink,  in  the  food  we 
eat,  in  the  soil  underfoot,  and  even  in  the  bodies  of  plants 
and  animals.     They  multiply  very  rapidly  by  cell  division 
and  in  some  cases  may  double  their  numbers  every  half  hour. 
It  is  due  to  their  activities  that  wood  rots,  food  ferments, 
and  cider  turns  to  vinegar. 

197.  Helpful  and  Harmful  Species. — Although  the  bacteria 
are  plants,  they  lack  the  green  coloring  matter  of  ordinary 
plants  and  thus  are  unable  to  make  food  for  themselves. 
Like  the  animals,  they  require  food  already  made,  and  this 
they  take  from  the  bodies  of  plants  and  animals,  living  or 
dead.     As  to  the  manner  in  which  food  is  obtained,  they  are 
divided  into  two  classes,  the  parasites,  which  obtain  their  food 
from  living  things,  and  the  saprophytes,  which  feed  only  upon 
dead  organic  matter.     In  using  the  food,  they  act  like  other 
living  things,  breaking  it  down  into  simpler  substances.     In 

231 


232  EXPERIMENTAL  GENERAL  SCIENCE 

this  way  they  usually  destroy  any  tissue  they  attack.  Nearly 
all  the  diseases  of  animals  and  plants  are  due  to  the  activities 
of  bacteria.  On  the  other  hand,  there  are  many  helpful  forms 
of  these  plants.  Certain  kinds  give  the  flavor  to  butter, 
cheese,  and  tobacco,  others  turn  cider  to  vinegar,  and  still 
others  cause  milk  to  sour.  The  retting  of  flax,  by  means  of 
which  the  fibers  for  linen  thread  are  obtained,  is  also  due  to 
the  action  of  bacteria.  Though  the  bacteria  of  decay  often 
injure  substances  which  we  value,  it  is  probable  that  even 
these  must  be  placed  among  the  helpful  forms.  To  realize 
the  helpfulness  of  such  forms,  we  have  only  to  consider  what 
would  happen  if  all  the  dead  leaves  and  other  refuse  which 
falls  on  the  earth  were  to  lie  where  they  fell  without  decaying. 


FIG.  85. — Various  forms  of  bacteria.     (Gager.) 

Moreover,  there  are  a  number  of  other  forms  in  the  soil  which 
steadily  break  up  organic  compounds  into  simpler  substances 
which  the  plants  can  use.  Others,  in  connection  with  the 
group  of  flowering  plants  called  legumes,  add  to  the  soil  in 
available  form  nitrogen  obtained  from  the  air. 

198.  Toxins  and  Ptomaines. — Bacteria  are  of  the  highest 
interest  to  man  because  of  the  capacity  for  harm  which  certain 
species  possess  if  allowed  to  thrive  unchecked.  When  growing 
in  protein  foods,  they  may  form  poisonous  substances  called 
ptomaines  which  are  very  difficult  to  neutralize.  Cooking 
the  food  may  kill  the  bacteria,  but  it  does  not  destroy  the 
ptomaines.  Other  forms  may  secure  entrance  into  the  human 
body  through  the  air  passages,  the  alimentary  canal,  or  through 
breaks  in  the  skin  due  to  abrasions  or  insect  bites,  and  so  cause 


BACTERIA  233 

disease.  Several  diseases  are  now  known  that  are  communi- 
cated to  man  and  other  animals  solely  through  the  bites  of 
insects.  In  the  body,  bacteria  may  break  down  the  cells,  or 
they  may  produce  substances,  known  as  toxins  which  rapidly 
poison  it.  In  some  cases,  a  colony  of  bacteria  in  a  limited 
part  of  the  body  may  produce  toxins  so  deadly  as  to  cause 
death  in  a  short  time. 

199.  Antitoxins. — In  most  cases,   when  a  body  is  being 
poisoned  by  toxins,  the  cells  form  antitoxins  to  counteract 
them.     The  antitoxins  kill  the  bacteria  and  so  free  the  body 
from  their  effects.     The  white  corpuscles  of  the  blood  also 
rapidly  destroy  bacteria.     Were  it  not  that  the  body  is  pro- 
tected in  this  way,  even  slight  injuries  would  prove  fatal. 
In  some  cases,  the  body  does  not  produce  its  antitoxin  fast 
enough  and  is  helped  in  its  work  by  the  injection  of  similar 
antitoxins  taken  from  other  animals.     The  antitoxin  used  in 
diphtheria  is  of  this  nature.     There  are  a  number  of  bacterial 
diseases  which  we  usually  have  only  once,  the  effects  of  the 
antitoxins  made  during  the  course  of  the  disease  seeming 
to  protect  the  body  from  other  attacks  of  it  through  life. 
The  individual  is  then  said  to  be  immune  to  that  disease. 
In  other  diseases,  the  effects  fail  after  a  time  and  the  disease 
may  then  be  taken  again.     A  number  of  serums  which  are 
practically  antitoxins  have  been  discovered  in  recent  years 
and  used  for  the  cure  of  disease.     These  are  made  from  the 
blood  of  other  animals  attacked  by  the  disease  or,  in  some 
cases,  from  the  bacteria  themselves. 

200.  Disinfectants    and    Antiseptics. — Since    bacteria  are 
plants,  they  may  be  destroyed  by  the  same  agencies  that  kill 
other  plants.     Drying  stops  the  activities  of  all  but  does  not 
kill  many  kinds.     They  simply  go  into  a  resting  condition  and 
revive  when  more  moisture  is  found.     Exposure  to  sunlight 
kills  many  species  and  exposure  to  extreme  cold,  like  drying, 
retards  their  activities  and  in  many  cases  kills  them.    The 


234  EXPERIMENTAL  GENERAL  SCIENCE 

surest  way  of  destroying  bacteria,  however,  is  to  subject  them 
to  great  heat,  either  by  boiling  or  steaming  them.  Even 
temperatures  much  below  the  boiling  point  have  been  found 
to  be  effective  in  the  case  of  many  kinds.  Milk  is  pasteurized 
by  being  brought  to  a  temperature  of  130°F.  and  held  at  that 
temperature  for  a  few  minutes.  Bacteria  are  also  rapidly 
destroyed  if  exposed  to  the  ultra-violet  rays,  and  chemicals 
of  various  kinds  are  also  effective.  Rendering  objects  free 
from  bacteria  is  called  sterilizing.  Chemicals  used  in  killing 
bacteria  are  usually  called  disinfectants.  In  the  human 
body,  however,  the  problem  of  destroying  bacteria  is  com- 
plicated by  the  necessity  of  killing  the  bacteria  without  injur- 
ing the  cells.  Substances  which  will  accomplish  this  are 
usually  called  antiseptics.  Among  substances  used  externally 
for  such  purposes  are  tincture  of  iodine,  boracic  acid,  carbolic 
acid,  hydrogen  peroxide,  bi-chloride  of  mercury,  and  alcohol. 
Salt,  sugar,  and  other  substances,  by  extracting  the  water 
from  bacteria,  affect  them  somewhat  as  ordinary  drying 
does.  Such  substances  are  often  called  preservatives. 

Practical  Exercises 
1.  Give  a  reason  for  washing  the  hands  before  eating. 


2.  Why  is  it  desirable  to  wash  thoroughly  food  that  has  been  exposed 
for  sale  in  the  open  market? 


3.  Why  are  cooked  foods  likely  to  be  more  wholesome  than  raw  foods? 


4.  Why  might  tea  or  coffee  made  from  a  suspected  water  be  less 
dangerous  than  the  water  itself? 


6.  Why  should  refrigerators  and  other  receptacles  for  food  be  fre- 
quently cleaned? 


BACTERIA  235 

6.  In  preserving  food  from  decay,  what  advantage  is  taken  of  the  fact 
that  plants  need  moisture  for  growth? 

7.  In  canning  foods,  why  is  it  necessary  to  bring  the  materials  to  a 
high  temperature? 

8.  Why  is  it  customary  to  seal  the  cans  containing  such  food? 


9.  Canned  foods  may  be  preserved  from  decay  if,  while  still  hot,  the 
jars  containing  them  are  closed  with  a  wad  of  cotton.     Explain. 


10.  In  preserving  foods  from  decay,  what  advantage  is  taken  of  the 
fact  that  plants  need  warmth  for  growth? 

11.  Why  do  canned  foods  soon  spoil  if  exposed  to  the  air? 

12.  Why  are  damp  rooms  undesirable  as  residences? 

13.  Why  are  cellars  and  other  poorly  lighted  places  undesirable  for 
residences? 

14.  Of  what  use  is  it  to  expose  bedding  to  the  sunlight? 

15.  Why  is  it  desirable  to  avoid  contact  or  association  with  persons 
who  are  suffering  with  disease? 

16.  Why  are  manufacturers  forbidden  to  use  certain  kinds  of  chemicals 
for  preserving  foods? 

17.  Make  a  list  of  the  antitoxins  of  which  you  have  heard. 

18.  Make  a  list  of  the  disinfectants  with  which  you  are  familiar  and 
check  those  which  may  be  used  as  antiseptics. 


236  EXPERIMENTAL   GENERAL   SCIENCE 

19.  Why  is  it  desirable  to  avoid  the  bites  of  mosquitos,  lice,  fleas  and 
the  like? 


20.  The  common  house-fly  does  not  bite.     Why  screen  it  from  our 
homes? 


21.  Why  are  dusty  places  undesirable  for  residences? 


CHAPTER  XXXIV 
THE  FRAMEWORK  OF  THE  BODY 

201.  The    Skeleton.— From    the    fact    that    the    simplest 
animals  have  no  skeleton,  we  perceive  that  the  possession  of 
such  a  structure  is  not  an  essential  characteristic  of  animal 
life,  though,  since  all  the  higher  types  possess  something  of  the 
kind,  it  apparently  plays  a  part  of  some  importance  in  the 
animal  body.     The  first  skeletons  were  external  and  were 
represented  by  such  structures  as  the  shell  of  the  clam,  the 
hard  outer  parts  of  the  lobster  and  crayfish,  and  the  horny 
covering  of  beetles  and  other  insects.     An  internal  skeleton 
is  found  only  in  the  group  called  vertebrates,  and  it  is  only 
in  this  group  that  true  bones  occur.     Man  being  the  highest 
representative  of  this  latter  group,  of  course,  has  one  of  the 
most  highly  developed  of  skeletons. 

202.  Arrangement  of  the  Skeleton. — The  skeleton  serves  as 
the  framework  of  the  body,  somewhat  analogous  to  the  wood 
and  bast  of  plants.     Its  chief  function  is  to  form  attachments 
for  the  muscles  and  thus  to  aid  in  producing  motion,  though 
it  also  serves  to  give  shape  and  strength  to  the  body  and  to 
protect  the  more  delicate  organs.     A  fundamental  pattern 
may   be   seen   in   the   skeletons   of   all   vertebrates,  though 
variously  modified  to  meet  individual  needs.     There  is  first 
of  all  an  axis  consisting  of  a  number  of  joints  or  vertebrce  which 
we  commonly  call  the  spine  or  back  bone.     In  man  there  are 
thirty-three  of  these  vertebrae,  though  in  adult  life  the  last 
nine  are  fused  together  into  what  appear  to  be  two  bones. 
In  the  lower  animals,  these  bones,  often  with  others,  form  the 
tail.     At  the  opposite  end  of  the  axis  are  twenty-two  irregular 

237 


238 


EXPERIMENTAL  GENERAL  SCIENCE 


Cranium. 


7  Cervical  vertebrae. 

Clavicle. 
Scapula. 


Humerus. 


Ilium. 

Ulna. 

Radius. 

Pelvis. 


Bones  of  the  carpus. 
Bones  of  the  metacarpus. 

Phalanges  of  fingers. 
Femur. 


Patella. 


Tibia. 
Fibula. 


Bones  of  the  tarsus, 
^ones  of  the  metatarsus. 
Phalanges  of  toes. 


FIG.  86.— The  skeleton.     (After  Holden.) 


THE  FRAMEWORK  OF  THE  BODY        239 

bones  forming  the  skull  or  framework  of  the  head  in  which  the 
organs  of  special  sense  are  located.  In  man  the  bones  of 
the  spinal  column  are  arranged  in  a  slight  double  curve  and 
the  column  itself  is  erect.  In  the  lower  animals  the  spinal 
column  is  usually  parallel  with  the  earth's  surface.  The  part 
which  includes  the  head  and,  in  all  vertebrates,  goes  first,  is 
called  the  anterior  portion  and  the  opposite  part  is  the  pos- 
terior. The  upper  side  is  the  dorsal  surface  and  the  under  side 
the  ventral  surface.  Attached  to  the  axis  are  usually  two 
girdles  of  bones  each  bearing  a  pair  of  appendages  or  limbs. 
In  man  these  appendages  are  called  arms  and  legs.  Between 
the  two  girdles  are  also  attached  in  pairs  a  number  of  curved 
bones  or  ribs.  Man  has  twelve  pairs  of  ribs,  all  of  which, 
excepting  the  last  two  pairs,  are  also  attached  in  front  to  the 
breast-bone,  which  is  really  three  bones  in  one.  These  bones 
thus  form  a  sort  of  bony  cage  in  which  are  the  heart  and  lungs. 
The  longest  bones  of  the  body  are  found  in  the  appendages. 
These  long  bones  are  nearly  cylindrical,  hollow  and  filled  with 
a  fatty  marrow  in  which  the  red  blood  corpuscles  are  formed. 
The  flat  bones,  such  as  the  ribs  and  the  bones  of  the  skull, 
have  no  central  cavity.  The  ends  of  the  bones  are  pitted  and 
ridged  for  the  attachment  of  the  muscles,  and  the  vertebrae 
have  various  bony  projections  for  this  purpose.  The  bones 
are  derived  from  cells  so  small  that  one  wonders  how  they 
can  form  a  substance  so  strong  as  bone:  the  same  may  be 
said  of  the  teeth.  The  bones  of  all  young  animals  are  very 
soft  and  flexible  at  birth  but  grow  harder  with  age.  This  ex- 
plains why  a  child  may  escape  without  broken  bones  from  a 
blow  that  would  seriously  injure  an  adult. 

203.  Joints. — The  bones  of  the  skeleton  are  joined  together 
in  a  variety  of  ways.  Those  of  the  cranium  (that  part  of  the 
skull  that  encloses  the  brain)  are  closely  and  immovably 
joined.  Such  joints  are  usually  called  sutures.  Other  joints 
are  constructed  on  the  familiar  hinge  pattern,  allowing  con- 


240  EXPEEIMENTAL  GENERAL  SCIENCE 

siderable  motion  in  one  plane ;  still  others  are  able  to  slide  over 
one  another  for  a  short  distance.  When  more  extended  move- 
ment is  required,  the  ball-and-socket  joint  may  be  found,  as 
at  the  shoulder  and  hip.  In  the  elbow  and  wrist,  there  is  a 
sort  of  rolling  joint  which  enables  us  to  turn  our  palms  out- 
ward. The  head  is  mounted  on  the  apex  of  the  spinal  column 
by  a  sort  of  rocking  joint  and  the  vertebra  supporting  the  head 
turns  part  way  around  on  a  pivot.  Great  freedom  of  motion 
is  possible  at  the  shoulder  from  the  fact  that  the  pectoral 
girdle  is  attached  only  indirectly  to  the  axis.  Strips  of  carti- 
lage attach  the  ribs  to  the  breast  bone  and  thus  permit  the 
chest  to  be  expanded  in  breathing. 

204.  Muscles,  Tendons  and  Ligaments. — The  parts  of  the 
skeleton  are  held  together  by  stout  ligaments  and  the  move- 
able  joints  are  padded  with  a  firm  substance  called  cartilage. 
All  of  the  spinal  vertebrse  are  separated  by  pads  of  this  sub- 
stance. The  muscles  and  tendons  also  aid  in  holding  the 
skeleton  together,  but  their  chief  use  is  to  produce  motion. 
In  animals  used  for  food,  we  recognize  the  muscles  as  lean 
meat  and  the  tendons,  ligaments,  and  cartilage  as  gristle. 
A  good  example  of  cartilage  may  be  found  in  the  hard  parts 
of  the  outer  ear  or  at  the  tip  of  the  nose.  The  soft  and  tender 
muscle  cells  are  bound  up  in  small  bundles  by  a  substance 
called  connective  tissue  and  these  bundles  combined  into  larger 
aggregations  form  the  muscles.  In  a  tough  piece  of  steak, 
the  whitish  fibers  running  through  it  are  sections  of  connec- 
tive tissue.  Toward  the  ends  of  the  muscle  the  strands  of 
connective  tissue  join  together  forming  the  stout  and  glisten- 
ing white  tendons  by  means  of  which  the  pull  of  the  muscles 
is  carried  across  the  joints.  In  moving  the  body,  the  bones 
and  muscles  act  much  like  the  ropes  and  arms  of  a  derrick. 
Each  end  of  a  muscle  is  attached  to  a  different  bone  and  thus 
when  the  muscle  contracts  and  shortens,  motion  of  one  bone 
or  the  other  is  produced.  It  is  the  simultaneous  contraction 


THE  FRAMEWORK  OF  THE  BODY         241 

of  all  the  muscle  fibers  that  causes  the  muscle  to  shorten.  The 
tendons  themselves  are  not  elastic.  There  are  nearly  300 
skeletal  muscles  in  the  body  and  they  occur  almost  invariably 
in  pairs,  thus  acting  as  antagonists  to  each  other.  One  pulls 
a  bone  in  one  direction  and  the  other  returns  it  to  its  original 
position.  Most  muscles  end  in  tendons,  but  all  do  not  do  so. 
The  diaphragm,  one  of  the  most  important  muscles  in  the  body, 
is  such  an  exception.  It  is  located  just  below  the  heart  and 
lungs  and  separates  the  body  cavity  into  two  chambers  called 
respectively  the  abdominal  and  thoracic  cavities.  Certain 
other  muscles  are  designed  to  regulate  the  size  of  various 
tubes  and  openings  and  are  known  as  sphincters.  Such  a 
muscle  is  found  where  the  stomach  opens  into  the  intestine. 

205.  Value  of  Exercise. — In  order  to  contract,  a  muscle 
must  receive  a  stimulus  from  the  brain.     When  a  stimulus 
thus  causes  a  muscle  to  contract,  it  remains  in  that  condition 
for  about  }{Q  of  a  second.     A  longer  period  of  contraction 
requires  additional  stimuli.     When  a  muscle  is  used  continu- 
ously for  a  time  it  becomes  fatigued  and  rest  is  necessary.     A 
change  of  work  which  puts  other  muscles  into  action  may  serve 
the  same  purpose  as  a  complete  rest.     Regular  exercise  is 
beneficial  to  the  muscles  since  it  educates  the  cells  to  work  in 
harmony  and  promotes  their  development.     Muscles  which 
are  used   regularly  are   larger,    firmer,   and   darker   colored 
than  those  which  are  not  so  used.     In  developing  the  muscles, 
a  little  exercise  each  day  is  much  better  than  more  vigorous 
exercise  at  irregular  intervals.     Rowing,  swimming,  walking, 
and  running  are  desirable  forms  of  exercise  because  they  call 
so  many  muscles  into  action.     Many  forms  of  exercise  are 
taken  for  the  pleasure  they  give,  such  as  walking,  dancing, 
skating,  and  many  of  the  games  played  by  children. 

206.  Breaks,  Sprains  and  Deformities. — When  a  bone  is 
broken,  it  must  be  held  immovably  in  one  position  until  the 
bone  cells  can  form  new  matter  with  which  to  knit  the  broken 

16 


242  EXPERIMENTAL  GENERAL  SCIENCE 

ends  together.  To  facilitate  this,  the  injured  member  is 
usually  bound  with  splints  or  enclosed  in  a  plaster  cast. 
When  the  break  is  a  slanting  one,  the  tension  of  the  muscles 
may  cause  one  part  of  the  bone  to  be  drawn  past  the  other,  in 
which  case  it  may  be  necessary  to  use  a  weight  to  hold  the 
ends  apart  and  prevent  the  bone  from  being  shorter  when 
repaired.  In  sprains,  the  ligaments  are  lessened,  strained, 
or  torn  from  their  fastenings,  and,  since  such  injuries  heal 
very  slowly,  sprains  often  prove  as  serious  as  broken  bones. 
The  best  remedy  for  a  serious  sprain  is  rest,  but  as  recovery  is 
made,  the  part  should  be  given  gradual  use  to  prevent  its 
becoming  stiffened.  When  bones  are  driven  from  their 
proper  positions  at  the  joints,  they  are  said  to  be  dislocated. 
In  youth,  the  parts  of  the  skeleton,  being  less  rigid  than  in 
later  life,  are  easily  bent  out  of  shape  and  this  may  result  in 
permanent  deformities.  Among  the  most  common  of  de- 
formities are  bow-legs,  round  shoulders,  and  crooked  spines. 
Children  may  be  made  bow-legged  by  being  encouraged  to 
walk  before  the  bones  are  strong  enough  to  support  their 
weight.  Round  shoulders  are  often  caused  by  bending  over 
a  book  or  other  work  for  too  long  a  time  or  by  sitting  at  desks 
that  are  too  low.  Crooked  spines  result  from  sitting  in  im- 
proper positions.  One  should  not  sit  too  long  in  one  position 
and  when  standing  should  maintain  an  erect  carriage.  If  one 
will  remember  to  " stand  tall,"  that  is,  to  stretch  up  to  the 
full  height,  much  will  have  been  done  to  avoid  an  awkward 
carriage.  Tight  clothing  over  the  ribs  may  cause  deformities 
which  are  harmful  because  they  interfere  with  correct  breath- 
ing, and  tight  shoes  may  result  in  bunions,  enlarged  joints, 
and  the  like.  High  heels  are  especially  to  be  avoided  since 
they  throw  the  weight  of  the  body  on  the  ankles  in  such  a  way 
as  to  make  them  thick  and  clumsy,  and  this  improper  dis- 
tribution of  the  weight  may  also  cause  broken  arches,  which 
result  in  flat  feet. 


THE  FRAMEWORK  OF  THE  BODY         243 

Practical  Exercises 

1.  How  many  joints  in  each  of  the  four  appendages  of  the  human 
skeleton? 


2.  How  many  bones  in   the   arm  (from  shoulder  to  elbow)?     How 
many  in  the  forearm  (from  elbow  to  wrist)  ? 

3.  Which  of  the  digits  (fingers  and  toes)  have  one  division  less  than 
the  others? 


4.  Which  section  of  the  lower  limb  corresponds  to  the  arm? 

5.  How  does  the  number  of  bones  in  the  forearm  compare  with  the 
corresponding  part  in  the  lower  limb? 


6.  What  difference  do  you  notice  in  the  direction  in  which  the  elbow 
and  knee  bend? 


7.  Clasp  the  arm  above  the  elbow  and  bring  the  forearm  up  to  the 
shoulder.     What  change  in  size  do  you  notice? 

8.  How  many  tendons  can  you  feel  on  the  inside  of  the  elbow  joint 
while  bending  it? 


9.  How  many  tendons  can  you  feel  under  the  knee  when  it  is  bent? 

10.  How  many  tendons  just  above  the  heel? 

11.  Can  the  ribs  move? 

12.  Which  has  the  greater  freedom  of  movement,  the  wrist  or  the 
ankle?     Why? 


13.  Name  the  kind  of  joint  illustrated  by  the  following:  shoulder 
knee,  wrist,  knuckles. 


244  EXPERIMENTAL   GENERAL   SCIENCE 

14.  In  the  lower  or  pelvic  girdle,  there  are  two  bones  called  the  pelvic 
or  hip  bones.     How  many  bones  in  the  pectoral  girdle  (at  the  shoulder)  ? 

16.  What  appendages  in  the  bird  correspond  to  the  human  arm? 

16.  How  do  the  bones  in  the  arm  and  forearm  compare  in  number  with 
the  bones  in  the  corresponding  parts  of  a  bird? 

17.  What  vertebrate  animals  lack  an  appendicular  skeleton? 

18.  Which  has  the  greater  freedom  of  motion,  the  thumb  or  the  great 
toe? 

19.  Of  what  advantage  is  this? 

20.  Examine  the  arm  and  forearm  and  locate  the  muscles  that  open 
and  close  the  hand. 

21.  Where  are  the  tendons  located  that  transmit  this  motion? 

22.  Why  are  the  bones  of  the  lower  extremities  larger  than  those  of  the 
upper? 

23.  Which  are  larger,  the  vertebrae  near  the  head  or  those  near  the 
hips?     Why? 

24.  Why  may  large  pillows  be  injurious? 

25.  The  muscles  on  the  breast  of  a  pigeon  are  dark  and  those  on  the 
breast  of  a  chicken  are  light.     Why? 

26.  Why  does  merely  standing  up  become  tiresome? 

27.  Which  is  less  tiresome,  a  long  walk  in  hilly  country  or  the  same 
distance  on  a  level?    Why? 


CHAPTER  XXXV 
THE  GOVERNOR  OF  THE  BODY 

207.  Need  of  a  Governor. — The  power  of  motion  is  inherent 
in  all  protoplasm,  but  when  this  protoplasm  is  arranged  in 
tissues  consisting  of  millions  of  cells,  it  is  impossible  to  con- 
ceive of  their  working  in  harmony  without  some  kind  of  a 
directing  force.  In  addition,  there  must  be  a  motor  impulse 
to  cause  the  cells  to  work  at  all.  Moreover,  since  the  motor 
impulse  comes  from  within,  there  must  be  some  means  of 
carrying  sensations  from  the  outside.  The  part  of  the  body 
charged  with  this  task  of  direction  is  the  nervous  system, 
which  consists  of  the  brain,  the  spinal  cord,  the  nerves,  and 
the  end  organs.  The  principal  parts  of  this  system  are  care- 
fully preserved  from  injury.  The  brain  is  enclosed  in  a  bony 
box,  the  cranium,  which  forms  part  of  the  skull,  and  is  pro- 
tected by  three  membranes ;  the  spinal  cord  runs  down  through 
a  series  of  bony  arches  formed  by  backward  projections  of  the 
vertebrae  and  the  large  nerves  are  deep  in  the  flesh,  close  to  the 
bones,  with  only  their  finer  divisions  coming  to  the  surface. 
There  are  twelve  pairs  of  these  nerves  given  off  by  the  brain 
and  thirty-one  given  off  by  the  spinal  cord.  Each  consists  of 
a  tract  over  which  sensations  travel  to  the  brain  and  a  tract 
over  which  motor  impulses  travel  from  the  brain  to  the 
muscles,  glands,  and  other  end  organs.  These  impulses  are 
similar  to  electricity  in  their  manifestations  and  travel  along 
the  nerves  at  the  rate  of  more  than  100  feet  a  second.  New 
impressions  may  originate  in  the  brain  and  be  carried  out  by 
impulses  sent  to  the  cells  in  various  parts  of  the  body,  but 
usually  some  disturbance  from  outside  stimulates  the  sensitive 

245 


246  EXPERIMENTAL   GENERAL   SCIENCE 

nerve  endings  and  a  sensation  is  carried  to  the  brain  which 
results  in  some  kind  of  motor  impulse  being  sent  to  the  muscles 
or  other  organs. 

208.  The  Brain. — The  upper  and  forward  part  of  the  brain 
is  known  as  the  cerebrum.     It  is  here  that  impulses  involving 
intelligence,  memory,  the  emotions,  and  the  will  originate. 
The  cerebrum  is  divided  by  a  deep  groove  into  a  right  and 
left  hemisphere  and  consists  of  white  and  gray  matter,  with  the 
gray  matter,  which  is  made  up  of  nerve  cells,  on  the  outside. 
Below  and  back  of  the  cerebrum  is  the  cerebellum  or  little  brain, 
whose  chief  function  is  to  coordinate  the  action  of  the  muscles 
and  cause  them  to  cooperate  properly  in  carrying  out  the 
directions  of  the  cerebrum.     Below  the  cerebellum,  where 
the  spinal  cord  connects  with  the  brain,  is  an  enlarged  portion, 
the  bulb  or  medulla  oblongata.     This  part,  in  addition  to  other 
functions,  controls  the  beating  of  the  heart,  breathing,  diges- 
tion, secretion,  and  other  processes  not  directly  under  control 
of  the  will. 

209.  The  Spinal  Cord. — The  spinal  cord  extends  down  along 
he  spinal  column  and,  like  the  other  parts  of  the  brain,  con- 
sists of  gray  and  white  matter,  though  in  this  instance  their 
positions  are  reversed,  the  white  matter  being  on  the  outside. 
The  white  matter  is  the  part  over  which  nervous  impulses 
travel  to  and  from  the  brain,  while  the  gray  matter  consists  of 
nerve  cells  which  enable  the  cord  to  act  like  the  brain  on 
occasion. 

210.  Involuntary  Action. — The  human  body  is  largely  auto- 
matic and  carries  on  many  of  its  processes  without  conscious 
effort,  in  fact,  over  most  of  the  functions  upon  which  depend 
the  health  and  well  being  of  the  body,  the  mind  has  no  control 
whatever.     In  some  cases,  such  as  breathing  and  winking,  we 
may  exercise  voluntary  control  for  a  short  time,  but  ultimately 
the  involuntary  centers  take  up  the  work.     By  taking  thought, 
we  may  increase  or  diminish  the  length  of  a  breath,  but  it 


THE  GOVERNOR  OP  THE  BODY          247 

would  be  impossible  to  hold  our  breath  until  we  suffocated. 
This  automatic  action  of  the  body  is  of  immense  advantage 
in  that  it  relieves  us  of  all  necessity  for  supervision  of  most, 
bodily  processes,  leaving  the  mind  free  to  attend  to  the  more 
important  matters  connected  with  mentality.  The  muscles 
under  the  control  of  the  will  are  very  different  in  appearance 
from  those  that  are  connected  with  involuntary  action.  The 
voluntary  muscles  are  striped  crosswise  of  their  length  while 
the  involuntary  muscles  are  plain.  Since  these  latter  are  not 
attached  to  the  bones  they  also  lack  tendons.  Their  move- 
ments are  controlled  largely  by  the  medulla  and  the  spinal 
cord,  but  some,  especially  those  of  the  heart,  have  some  power 
to  contract  and  expand  by  themselves. 

211.  Reflex  Action. — The  spinal  cord    not  only  transmits 
nervous  impulses  to  and  from  the  brain,  but  it  may  act  like 
the  brain  on  occasion  and  send  out  impulses  in  response  to 
sensations  without  waiting  for  the  brain  to  act.     Thus,  when 
a  finger  is  injured,  we  pull  it  out  of  danger  before  we  can  think 
about  the  matter.     Sensations  may  even  cause  such  actions 
in  distant  and  different  parts  of  the  body,  as  when  a  tickling 
in  the  nose  causes  us  to  sneeze  or  some  disagreeable  sight  or 
sound  may  cause  fainting.     Actions  of  this  kind  are  called 
reflex  actions.     Many  acts  which  are  conscious  and  voluntary 
at  the  beginning  may  later  become  reflex,  as  in  walking,  skat- 
ing, bicycling,  and  even  piano  playing.     Such  actions,  though 
ordinarily  reflex,  may,  however,  be  controlled  by  the  will. 
The  actions  of  many  animals  are  reflex  and  the  lower  the 
animal  in  the  scale  of  life,  the  less  important  do  the  higher 
centers  of  the  brain  become.     The  advantages  of  reflex  action 
are  that  they  automatically  withdraw  the  body  from  injury 
and,  like  the  involuntary  actions,  relieve  the  higher  nerve 
centers  of  the  routine  work  of  running  the  body. 

212.  Pain  and  the  Nerves. — Pain  may  be  regarded  as  an 
over  stimulation   of  the  end   organs.     The  sensations  are 


248  EXPERIMENTAL   GENERAL   SCIENCE 

carried  to  the  brain  by  the  nerves,  but  the  nerves  themselves 
are  insensible  to  such  sensations.  When  a  nerve  is  cut  or 
otherwise  injured,  it  sends  a  sensation  such  as  it  ordinarily 
sends  to  the  brain,  and  this  is  referred  back  to  the  end  organs 
of  the  nerve,  though  these  may  perhaps  be  a  long  way  from 
the  injury.  Cutting  the  nerve  which  carries  the  sensation  of 
sight  to  the  eye  would  give  the  sensation  of  a  blinding  flash 
of  light,  but  the  nerve  would  feel  no  pain.  The  seat  of  sensa- 
tion, therefore,  is  in  the  brain.  If  the  part  of  a  nerve  which 
carries  sensations  from  any  part  of  the  body  to  the  brain  be 
cut,  all  further  sensation  in  that  part  of  the  body  will  be  lost 
but  it  may  still  be  capable  of  motion.  If  the  part  of  a  nerve 
that  carries  motor  impulses  from  the  brain  be  cut,  all  motion 
in  that  part  of  the  body  served  by  the  nerve  will  cease.  Al- 
though all  sensations  are  felt  in  the  brain  alone,  this  organ  is 
insensible  to  injuries  to  itself  and  may  be  cut  without  causing 
pain. 

213.  Sleep. — Like  the  muscles,  the  brain  is  improved  by 
proper  exercise.  Hard  study  for  a  reasonable  length  of  time 
is  not  harmful,  but  such  study  for  prolonged  intervals,  or 
carried  on  late  at  night  when  the  brain  should  be  resting,  is 
objectionable.  After  a  long  period  of  work  with  the  brain, 
the  cells  have  a  shrunken  appearance  and  a  period  of  rest  is 
required  to  restore  them  to  their  normal  condition.  The 
best  rest  for  the  brain  is  sleep.  An  adult  requires  from  seven 
to  eight  hours  of  sleep  daily  and  growing  children  require 
somewhat  more.  Healthy  babies  sleep  a  large  part  of  each 
day.  It  appears  to  make  no  difference  whether  one  sleeps 
in  the  daytime  or  at  night,  provided  the  period  of  sleep  is 
uninterrupted.  Night,  however,  is  usually  the  better  time 
because  of  the  greater  quiet. 

Practical  Exercises 

1.  Cross  your  first  and  middle  fingers  and  touch  your  nose  with  them. 
Why  does  it  feel  like  two  noses? 


THE  GOVERNOR  OF  THE  BODY          249 

2.  The  "funny  bone"  is  the  name  given  to  the  place  on  the  outside 
of  the  elbow  where  the  nerve  passes  over  the  joint.     Why  does  bumping 
this  cause  a  tingling  sensation  in  the  fingers? 

3.  When  a  portion  of  a  limb  has  been  amputated,  the  victim  often 
complains  of  pains  in  the  lost  member.     Explain. 

• 

4.  Why  may  a  sharp  blow  on  the  head  cause  one  to  "see  stars?" 

5.  What  part  of  the  nervous  system  guides  one  who  walks  in  his 
sleep? 

6.  Why  cannot  one  sleep  standing  up? 

7.  What  part  of  the  brain  is  educated  in  learning  to  play  the  piano? 

8.  When  one  falls  asleep  in  his  chair  why  does  his  head  drop  forward  ? 

9.  What  part  of  the  brain  is  educated  by  a  history  lesson? 

10.  When  one's  finger  is  burned,  where  is  the  pain? 


CHAPTER  XXXVI 
THE  NOURISHMENT  OF  THE  BODY 

214.  The  Need  of  Food. — The  human  body  is  like  all  other 
machines  in  that  it  cannot  work  without  energy.     It  also 
requires  more  or  less  material  for  growth  and  repair  (§179). 
The  material  that  supplies  these  needs  are  comprised  under 
the  general  name  of  foods.     Water,  oxygen,  and  various  salts 
are  sometimes  included  in  the  list  of  foods,  since  they  are 
needed  by  the  body,  but  they  are  not  foods  in  the  usual  sense, 
and  we  will  here  confine  our  attention  to  those  substances 
more  commonly  regarded  as  such  and  classed  as  proteins, 
fats,   and   carbohydrates,    respectively   (§180).     These   sub- 
stances, as  they  occur  in  the  bodies  of  animals  and  plants  used 
for  food,  cannot  be  assimilated  by  the  human  body  until 
they  have  undergone  certain  chemical  changes  which  render 
them  soluble  and  otherwise  fit  them  for  being  absorbed. 
Such  changes  are  involved  in  the  processes  of  digestion  and 
seem  in  large  measure  to  be  due  to  the  breaking  up  of  large 
molecules  into  smaller  ones  by  means  of  certain  ferments 
known    as    enzymes.     In  digestion,  the    enzymes   act   some- 
what  as    catalyzers    do    in    other    chemical    reactions   and 
cause  the  digestive  processes  to  continue  without  being  used 
up  themselves. 

215.  Value  of  Foods. — The  carbohydrates,  such  as  starch 
and  sugar,  and  the  fats,  are  the  chief  sources  of  food  for  the 
body.     Energy  may  be  derived  from  the  proteins,  it  is  true, 
but  this  is  not  an  economical  use  of  such  foods.     They  are 
more  useful  in  the  growth  and  repair  of  the  body.     In  order 
to  derive  enough  energy  from  proteins,  an  unusual  amount 

250 


THE  NOURISHMENT  OP  THE  BODY        251 

would  have  to  be  eaten.  As  a  matter  of  fact,  we  commonly 
use  a  combination  of  foods  in  our  diet,  if  allowed  a  choice, 
which  includes  representatives  of  the  three  classes  of  foods. 
Combinations  of  this  kind  are  bread  and  butter,  rice  and  milk, 
pork  and  beans,  potatoes  and  meat,  etc.  The  ratio  of  proteins 
to  carbohydrates  in  the  ordinary  food  should  be  about  1  to 
6.  Fats,  which  contain  more  carbon  in  proportion  to  the  oxy- 
gen than  do  carbohydrates,  are  useful  sources  of  heat,  and  in 
cold  countries,  and  in  the  colder  months  of  our  year,  have  an 
increased  representation  in  our  food.  Certain  articles  of  food 
are  of  much  greater  value  in  sustaining  life  than  others. 
Among  those  of  greatest  value  are  corn,  beans,  peas,  potatoes, 
and  the  various  grains.  Nuts  have  a  high  food  value  because 
of  the  oil  and  proteins  they  contain.  Cucumbers,  lettuce, 
spinach,  and  radishes  contain  very  little  food  material  but  are 
valuable  for  the  mineral  salts  which  they  contain  and  for  giving 
bulk  to  the  food.  Most  fruits  are  of  little  value  as  nourish- 
ment, though  the  acids,  salts,  and  flavors  found  in  them  make 
them  most  desirable  additions  to  our  food  supply.  The  value 
of  a  food  is  usually  measured  by  the  number  of  kilocalories  it 
contains,  a  kilocalorie  being  defined  as  a  thousand  ordinary 
calories.  In  books  on  food,  this  unit  is  spoken  of  simply  as 
calorie,  but  the  kilocalorie  is  always  meant.  Those  who  work 
hard  with  their  muscles  require  enough  food  to  give  about 
5000  kilocalories  daily.  Students  and  those  whose  occupa- 
tions do  not  require  vigorous  exercise  need  much  less.  High 
school  students  need  about  2500  kilocalories  daily. 

216.  The  Digestive  System. — In  the  one-celled  animals, 
each  cell,  of  course,  secures  and  digests  its  own  food,  but  in 
the  more  complex  animals  which  often  contain  many  billions 
of  cells,  the  majority  of  which  cannot  come  unto  direct  con- 
tact with  the  food,  means  must  be  provided  for  securing  and 
transporting  this  food  to  them.  Digestion  is  therefore  carried 
on  by  certain  cells  for  the  entire  body  and  the  material 


252 


EXPERIMENTAL  GENERAL   SCIENCE 


NASAL  CAVITV 
PALATE 

MOUTH 

TONGUE 


NASAL  PHARYNX 

ORAL  PHARYNX 
LARYNGEAL  PHARYNX 


BILE  AND 

PANCREATIC 

DUCTS 


RIGHT  COLIC 
FLEXURE 


DUODENUM 


LEFT  COLIC 
FLEXURE 


PROCESS 

FIG.  87. — Diagram  of  the  alimentary  canal.     (Morris.) 


THE  NOURISHMENT  OF  THE  BODY         253 

transported  to  the  distant  cells.  That  part  of  the  body  in 
which  food  is  digested  is  called  the  alimentary  canal.  The 
simplest  digestive  system  is  a  mere  sac  or  stomach  into  which 
food  is  taken,  the  available  material  selected,  and  the  refuse 
thrown  out.  The  more  complex  animals,  including  man,  have 
a  tube  extending  through  the  body  along  which  the  food 
slowly  moves  while  substances  are  absorbed  from  it.  During 
its  passage  through  the  alimentary  canal,  digestive  juices  are 
poured  over  the  food,  thus  rendering  it  soluble  and  capable 
of  being  absorbed.  The  movement  of  the  food  is  caused  by 
rhythmic  contractions  of  the  walls  of  the  alimentary  canal 
which  forces  the  contents  of  the  canal  onward. 

217.  Structure  of  the  Alimentary  Canal. — The  alimentary 
canal  in  general  consists  of  an  outer  layer  of  muscles  and  con- 
nective tissue  and  a  lining  of  mucous  membrane,  the  latter  so 
called  because  it  secretes  a  glairy  liquid,  called  mucus,  which 
lubricates  it.  This  membrane  is  much  like  the  outer  layer  of 
the  skin  in  structure  and  originates  from  the  same  tissue. 
There  are  considerable  differences  in  the  digestive  organs  of 
the  different  groups  of  animals,  due  in  part  to  the  kind  of  food 
they  take  and  the  kind  of  structures  to  be  nourished,  but  all 
are  essentially  alike.  In  the  vertebrates,  there  is  first  a 
mouth  for  taking  the  food,  usually  equipped  with  teeth  for 
tearing  or  grinding  it  into  small  pieces,  and  a  tongue  for 
moving  it  about  during  the  process  of  chewing.  The  mouth 
opens  into  the  throat  from  which  a  tube,  the  esophagus,  leads 
to  the  stomach,  the  latter  largely  a  storage  organ.  Beyond  the 
stomach  is  an  intestine  in  which  the  greater  part  of  the  food 
is  digested  and  from  which  it  is  absorbed.  The  stomach  lies 
crosswise  of  the  body  just  below  the  diaphragm.  Ordinarily 
it  holds  about  three  pints  but  it  may  be  distended  to  hold  more. 
In  man,  the  intestine  is  divided  into  two  regions,  the  small 
intestine  and  large  intestine  respectively.  The  small  intestine 
begins  at  the  stomach  on  the  right  side  of  the  body  and  owing 


254  EXPERIMENTAL  GENERAL  SCIENCE 

to  its  length,  is  much  bent  and  coiled.  It  occupies  most  of  the 
abdomen.  The  combined  length  of  the  two  intestines  is  nearly 
thirty  feet.  The  small  intestine  empties  into  the  large  intes- 
tine at  the  lower  right  side  of  the  body.  Near  this  point, 
a  small  tube  two  or  three  inches  long,  called  the  appendix, 
projects  downward  from  the  large  intestine.  This  is  often  the 
seat  of  a  serious  inflammation  called  appendicitis.  The  large 
intestine  passes  upward  on  the  right  side,  across  the  body 
below  the  stomach  and  downward  on  the  left  side  and  so  on 
to  the  surface  of  the  body.  In  all  animals,  no  matter  what  the 
structure  of  the  alimentary  canal,  it  invariably  begins  in  the 
head  with  the  mouth. 

218.  Digestive  Juices. — When  food  is  taken  into  the 
mouth  it  is  mixed  with  the  saliva,  a  juice  poured  out  by  six 
glands,  three  on  each  side  of  the  head.  The  glands  are  simply 
groups  of  cells  which  have  the  power  to  secrete  saliva,  the 
material  for  which  is  taken  from  the  blood.  The  disease  called 
mumps  is  caused  by  an  inflammation  of  some  of  these  glands. 
The  chief  use  of  the  saliva  is  to  moisten  the  food  and  facilitate 
its  passage  through  the  throat  and  esophagus  to  the  stomach, 
though  it  also  contains  a  ferment  called  ptyalin  which  changes 
some  of  the  starch  in  the  food  to  sugar.  In  the  stomach  the 
food  comes  in  contact  with  the  gastric  juice  and,  by  a  peculiar 
churning  movement  of  the  stomach  walls,  is  thoroughly  mixed 
with  it.  The  gastric  juice  contains  pepsin  and  rennin  as 
well  as  about  .02  per  cent,  of  hydrochloric  acid.  The  acid  kills 
many  germs  in  the  food  and  renders  the  contents  of  the 
stomach  acid,  thus  promoting  the  working  of  the  enzymes  in 
the  gastric  juice  which  cease  their  activities  in  an  alkaline 
medium.  The  pepsin  changes  some  of  the  protein  to  more 
soluble  forms  called  peptones  and  also  prepares  the  fats  for 
digestion  by  breaking  up  the  tiny  pouches  in  which  they  are 
found.  The  rennin  curdles  milk.  As  the  food,  now  a  thin, 
watery  mixture,  passes  into  the  small  intestine,  the  powerful 


THE  NOURISHMENT  OF  THE  BODY        255 

pancreatic  juice  is  poured  into  it.  This  juice  is  secreted  by  the 
pancreas,  a  gland  located  beneath  the  stomach  in  a  bend  of 
the  intestine.  In  animals  used  for  food,  these  glands  are  often 
known  as  sweetbreads.  The  pancreatic  juice  has  three  fer- 
ments or  enzymes,  namely  amylopsin  which  digests  starch, 
trypsin  which  digests  proteins,  and  steapsin  which  emulsifies 
the  fats  by  breaking  them  up  into  fatty  acids  and  glycerine 
and  then,  by  combining  them  with  alkalis,  changing  them 
into  soaps.  The  pancreatic  juice,  therefore,  is  the  most 
important  digestive  fluid  in  the  body.  When  the  pancreas 
does  not  function  properly,  it  causes  the  disease  known  as 
diabetes.  The  contents  of  the  stomach  are  acid  (§122,  123), 
but  the  pancreatic  juice  can  work  only  in  an  alkaline  medium. 
The  neutralization  of  the  food  after  it  leaves  the  stomach  is 
accomplished  by  the  bile,  a  strongly  alkaline,  yellowish  fluid 
poured  into  the  intestine  by  the  liver.  The  liver  is  a  dark  red 
gland  located  on  the  right  side  of  the  body  below  the  dia- 
phragm. On  the  underside  of  the  liver  is  a  small  sac,  the  gall 
bladder,  in  which  bile  is  stored  when  not  needed  in  digestion. 
The  small  intestine  also  secretes  a  digestive  juice,  but  it  appears 
to  be  of  little  importance.  The  digestive  juices  are  all  pro- 
duced by  glands  whose  action  is  controlled  by  that  part  of  the 
nervous  system  not  subject  to  the  will.  Many  of  their 
processes  are  the  result  of  reflex  action.  Often  the  sight  or 
smell  of  food  will  cause  the  glands  to  begin  their  secretions. 
It  is  due  to  this  cause  that  the  mouth  "waters"  at  the  thought 
of  a  particularly  pleasing  food.  Under  fear,  grief,  or  strong 
excitement,  the  glands  do  not  always  produce  a  sufficient 
amount  of  their  secretions,  and  if  one  takes  food  at  such  times 
he  may  suffer  from  indigestion. 

219.  The  Teeth. — Only  the  more  complex  animals  have 
teeth,  though  all  but  the  simplest  have  some  means  of  grind- 
ing their  food.  Those  forms  which  lack  teeth  have  horny 
jaws,  beaks,  mandibles,  or  other  organs  made  from  thickened 


256 


EXPERIMENTAL   GENERAL   SCIENCE 


portions  of  the  skin.  In  fact,  the  teeth,  though  considerably 
harder  than  bone,  are  really  hardened  portions  of  the  skin. 
In  man  there  are  two  sets  of  teeth,  the  first  set  or  "milk  teeth" 
being  twenty  in  number  and  the  second  or  permanent  set 
containing  thirty-two.  There  are  the  same  number  of  teeth 
in  each  jaw  and  the  same  number  on  each  side  of  the  jaw.  The 
first  set  consists  of  four  chisel-like  incisors  in  front  in  each 
jaw.  Back  of  these  on  each  side  is  a  single  strong  canine 


FIG.  88. — The  temporary  teeth.     The  rudiments  of  the  permanent  teeth  are 
seen  enclosed  in  the  bones.     (Gorgas.) 

(cuspid)  tooth  and  back  of  the  canines  two  teeth  with  flattened 
surfaces  for  grinding  and  called  molars  in  consequence.  The 
milk  teeth  fall  out  one  by  one  and  are  succeeded  by  stronger 
teeth  of  the  same  kind.  In  this  permanent  set,  three  larger 
grinding  teeth  or  "back  teeth"  make  their  appearance  further 
back  on  each  side  of  the  jaw.  The  last  of  these  are  sometimes 
called  wisdom  teeth.  All  the  teeth  are  firmly  set  in  the  jaw 
and  all  are  supplied  with  nerves  and  blood  vessels  which  run 


THE  NOURISHMENT  OF  THE  BODY        257 

up  through  the  roots  to  the  sensitive  pulp  within.  When, 
through  decay,  the  pulp  or  nerve  is  exposed,  toothache  is  the 
result.  To  preserve  the  teeth,  they  should  be  brushed  at 
least  once  daily  with  a  good  stiff  brush  in  order  to  remove 
particles  of  food  which  otherwise  would  cause  them  to  decay. 
If  the  teeth  are  not  cleaned  after  every  meal,  the  best  time  to 
brush  them  is  after  the  evening  meal.  When  the  teeth  begin 
to  decay,  the  dentist  should  be  visited  before  the  trouble  has 
proceeded  far  enough  to  cause  the  tooth  to  ache.  The  tooth 
can  then  be  treated  without  pain.  It  is  a  good  plan  to  have 
the  teeth  inspected  by  a  dentist  at  least  twice  a  year  in  order 
that  any  beginning  decay  may  be  noticed  in  time. 

Practical  Exercises 

1.  How  do  clothes  and  shelter  enable  us  to  economize  food? 

2.  Why  may  bad  news  cause  us  to  lose  our  appetite? 


3.  Pick  out  the  chief  food  constituents  in  the  following  food  combina- 
tions :  bread  and  butter,  mush  and  milk,  pork  and  beans,  pancakes  and 
sausage,  macaroni  and  cheese,  roast   pork  and  apple-sauce,  roast  beef 
and  mashed  potatoes. 

4.  Chew  a  crust  of  bread  for  a  long  time  and  explain  the  sweet  taste 
that  develops. 


5.  Why  may  the  sight  of  a  person  eating  a  lemon  cause  the  mouth  to 
water? 


6.  With  a  dull  knife,  scrape  some  cells  from  the  inside  of  the  cheek  and 
examine  with  the  microscope.  What  is  their  shape?  Locate  the 
nucleus. 


7.  Which  of  the  milk  teeth  are  first  to  appear? 

17 


258  EXPERIMENTAL   GENERAL   SCIENCE 

8.  Where  do  the  first  of  the  permanent  teeth  appear? 

9.  Which  have  the  larger  roots,  the  milk  teeth  or  the  permanent  set? 

10.  Which  of  the  milk  teeth  are  first  to  fall  out? 

11.  If  you  have  lost  a  tooth,  or  have  one  that  is  decayed,  locate  it. 

12.  Why  do  the  edges  of  the  upper  and  lower  incisors  not  meet? 

13.  How  do  you  explain  the  Eskimo's  fondness  for  fats? 


CHAPTER  XXXVII 
THE  TRANSPORTING  SYSTEM  OF  THE  BODY 

220.  The  Blood.— After  the  food  has  been  digested  it  still 
remains  to  be  distributed  throughout  the  body  to  the  cells 
which  need  it.  The  office  of  distribution  is  performed  by  the 
blood,  a  watery  fluid,  yellowish  in  color,  in  which  float  a  vast 


FIG.  89. — Corpuscles  of  blood,  as  seen  under  the  microscope.  Four  white 
ones  are  shown.  The  red  ones  have  a  tendency  to  form  rows.  (Funke  and 
Brubaker.) 

number  of  very  minute  pinkish  disks  known  as  red  blood 
corpuscles.  The  watery  part  of  the  blood  is  the  plasma.  In 
a  cubic  millimeter  of  blood,  which  is  much  less  than  a  drop, 
there  are  more  than  five  million  corpuscles.  These  corpuscles 
are  really  cells,  though  they  lack  the  customary  nucleus.  In 

259 


260  EXPERIMENTAL   GENERAL   SCIENCE 

the  blood  of  the  lower  animals,  however,  the  corpuscles  are 
nucleated.  There  are  also  to  be  found  in  the  blood  certain 
larger  globular  cells  called  white  blood  corpuscles.  These  are 
greatly  outnumbered  by  the  red  corpuscles,  often  as  much  as 
300  to  1.  The  blood  is  contained  in  a  closed  system  of  tubes 
called  blood  vessels  and  is  kept  in  constant  motion  through  the 
body  by  a  sort  of  double  pump,  the  heart.  The  tubes  which 
carry  the  blood  away  from  the  heart  are  known  as  arteries, 
and  those  which  return  it  to  the  heart  are  veins.  The  blood 
leaves  the  heart  for  its  tour  of  the  body  through  a  single  large 
artery,  the  aorta.  This  soon  branches  into  many  divisions 
which  go  to  all  parts  of  the  body.  As  they  subdivide  they  be- 
come smaller  and  smaller  until  finally  the  corpuscles,  minute  as 
they  are,  have  to  squeeze  to  get  through  them.  These  very 
small  tubes  are  called  capillaries.  From  the  capillaries,  the 
blood  flows  into  somewhat  larger  tubes,  called  veins,  and  these 
flow  into  still  larger  ones  until  two  main  veins  return  the  blood 
to  the  heart.  One  may  get  an  idea  of  how  very  numerous  the 
capillaries  are  by  reflecting  that  the  slightest  break  in  the 
flesh  will  injure  the  capillaries  and  allow  some  of  the  blood  to 
run  out.  The  arteries  are  usually  deep  in  the  flesh  and  rarely 
come  to  the  surface  except  where  they  cross  a  joint,  but  many 
of  the  veins  are  nearer  the  surface  and  may  be  seen  through  the 
skin. 

221.  Absorption. — Water  and  mineral  salts  may  be  absorbed 
from  any  part  of  the  alimentary  canal,  but  the  bulk  of  the 
food  is  absorbed  by  the  blood  vessels  of  the  small  intestine. 
The  walls  of  the  intestine  are  abundantly  supplied  with  blood 
vessels  and  the  food  passes  into  them  by  osmosis  (§102). 
In  order  to  pass  into  the  blood  in  this  way,  starch  has  to  be 
changed  to  sugar  and  other  sugars  have  to  be  changed  to 
grape  sugar.  Peptones,  as  such,  are  not  found  in  the  blood 
and  therefore  appear  to  undergo  a  second  change  in  their 
passage  through  the  mucous  membrane  and  the  walls  of  the 


THE  TRANSPORTING  SYSTEM  OF  THE  BODY    261 

intestine.  The  fats  are  absorbed  by  a  special  set  of  tubes, 
the  lacteals,  so  called  because  their  contents  have  a  milky 
appearance.  The  lacteals  end  in  certain  minute  but  numerous 
projections  in  the  small  intestine  known  as  villi.  It  is  through 
the  walls  of  the  villi  that  the  emulsified  fats  are  absorbed. 
The  contents  of  the  lacteals  empty  into  the  thoracic  duct, 
a  tube  about  as  large  as  a  goosequill  which  extends  up  through 
the  thorax  and  empties  into  the  general  circulation  under  the 
left  collar  bone.  The  blood  supply  to  the  stomach  and  in- 
testines does  not  return  at  once  to  the  heart  but  flows  into  a 
larger  vein,  the  portal  vein,  which  goes  to  the  liver.  Here  it 
again  passes  through  a  set  of  capillaries  where  much  of  its 
carbohydrate  food  is  withdrawn  and  stored  in  the  form  of 
glycogen,  a  kind  of  animal  starch.  Glycogen  is  also  found  in 
the  muscles. 

222.  Functions  of  the  Blood. — The  digested  food  used  by 
the  cells  is  carried  to  them  by  the  plasma  and  by  them  built 
up  into  new  tissues  or  oxidized  to  produce  energy.  Since  the 
blood  vessels  form  a  closed  system,  the  plasma,  in  order  to 
reach  the  cells,  soaks  out  through  the  walls  of  the  capillaries 
into  the  spaces  between  the  cells.  In  this  condition  it  is 
known  as  lymph.  The  lymph  is  carried  back  to  the  circula- 
tion through  tubes  that  empty  into  the  right  and  left  sub- 
clavian  veins  near  the  throat.  The  red  corpuscles  act  as  car- 
riers between  the  cells  and  the  lungs,  bringing  oxygen  to  the 
cells  and  carrying  away  the  carbon  dioxide  produced  in  respira- 
tion. They  are  able  to  do  this  by  means  of  the  red  coloring 
matter,  or  haemoglobin,  which  they  contain.  This  substance 
combines  with  both  oxygen  and  carbon  dioxide  and  absorbs 
whichever  is  more  abundant.  The  white  corpuscles  act  some- 
what like  scavengers,  wandering  here  and  there  and  destroying 
bacteria  and  other  harmful  matter  wherever  met.  They  have 
a  sort  of  slow  movement  of  their  own  and  can  pass  through  the 
walls  of  the  capillaries  in  their  search  for  employment.  Here 


262 


EXPERIMENTAL   GENERAL   SCIENCE 


and  there  along  the  lymphatic  tubes  are  spongy  bodies  called 
glands  or  nodes  in  which  the  white  corpuscles  are  formed.  The 
glands  also  retard  the  passage  of  bacteria  through  them 
and  when  an  adjacent  part  is  invaded  by  bacteria  may  be- 
come swollen  and  tender  to  the  touch.  They  are  often  called 
kernels  when  noticed  under  the  arms  or  about  the  throat. 

223.  The  Heart. — The  heart  is  a  hollow,  pear-shaped  organ 
composed  of  muscle,  and  is  about  the  size  of  the  fist.  It  is 
located  in  the  center  of  the  thorax  between  the  lungs,  but 
since  the  lower  part  is  tipped  somewhat  to  the  left,  the  beating 


FIG.  90. — White  corpuscles  penetrating  capillary  walls. 
and  Stirling.) 


(Landois 


is  felt  between  the  fifth  and  sixth  ribs  on  the  left  side.  The 
heart  has  four  chambers,  two  for  pumping  the  blood  and  two 
which  act  as  receiving  chambers  for  it  as  it  returns  to  the 
heart.  The  heart  is  suspended  in  the  thoracic  cavity  and 
the  blood  vessels  connect  with  it  at  the  upper  side.  It  beats 
or  contracts  rhythmically  as  long  as  the  body  is  alive  and  gets 
its  rest  for  a  short  period  between  each  beat.  In  infancy,  the 
heart  beats  about  140  times  a  minute,  in  youth  the  rate  is 
from  90  to  100  and  in  adult  life  it  is  from  70  to  75.  These 
pulsations  may  be  felt  in  various  parts  of  the  body  where  the 


THE    TRANSPORTING    SYSTEM   OF   THE  BODY 


263 


arteries  approach  the  surface.  The  normal  rate  at  which 
the  heart  beats  may  be  affected  in  various  ways.  It  quickens 
with  excitement  and  exercise  and  slows  down  during  sleep  or 
even  when  one  lies  down. 

224.  Circulation  of  the  Blood. — The  heart  is  practically  two 
pumps  in  one,  the  right  half  being  concerned  with  pumping 
the  blood  to  the  lungs  and 
the  left  half  sending  it  on  its 
tour  through  the  body.  The 
blood  returns  from  the  body 
through  two  veins,  the  vence 
cavce,  and  enters  the  right 
upper  chamber,  the  right 
auricle.  From  this  it  de- 
scends into  another  chamber, 
the  right  ventricle,  which  con- 
tracts much  like  the  bulb  of 
an  atomizer  and  forces  the 
blood  through  the  lungs. 
From  the  lungs  it  flows  back 
to  the  heart,  entering  the  left 
auricle  and  flowing  into  the 
left  ventricle  whence  it  is  again 
forced  out  through  the  body. 
At  the  point  where  the  aorta 
leaves  the  heart,  a  set  of  valves 
prevents  the  blood  from  flow- 
ing back  to  the  heart.  There  are  no  other  valves  in  the 
arteries.  The  walls  of  the  arteries,  being  elastic,  dilate  as  each 
successive  heart  beat  adds  more  blood  to  their  store  and,  while 
the  heart  is  resting  for  another  beat,  contract  and  force  the 
blood  along  to  the  capillaries.  In  old  age  and  in  certain 
diseases,  the  arteries  lose  some  of  their  elasticity  and  thus  fail  to 
expand  as  more  blood  is  forced  into  them,  causing  the  blood 


FIG.  91.— The  heart. 


VEINS 

(After  Bundy.} 


264 


EXPERIMENTAL   GENERAL   SCIENCE 


—ARTERIES 
minium  VEINS 


FIG.  92. — Scheme  of  the  circulation.     (After  Bundy.) 


THE   TRANSPORTING   SYSTEM   OF  THE  BODY         265 

pressure  to  increase  often  to  a  dangerous  point.  The  im- 
mense number  of  capillaries  into  which  the  arteries  divide 
distributes  and  lessens  the  pulsations  of  the  heart  and  when 
the  blood  reaches  the  veins  it  shows  no  pulsations.  The 
blood  flows  through  the  veins  largely  by  reason  of  the  pressure 
from  the  heart,  though  the  veins  have  valves  at  frequent 
intervals  which  oblige  the  blood  to  flow  in  only  one  direction. 
Each  movement  of  the  muscles,  therefore,  aids  in  compressing 
the  veins  and  forcing  the  blood  onward. 

225.  Regulation  of  the  Blood  Stream. — Vigorous  exercise 
increases  the  heart  beat  and  more  blood  reaches  all  parts  of 
the  body  in  a  given  time,  but  the  blood  does  not  ordinarily 
flow  in  unvarying  quantity  to  each  tissue  and  organ.     In- 
stead, the  flow  is  automatically  controlled  by  the  nervous 
system  in  such  a  way  that  the  parts  needing  the  greatest 
supply  shall  receive  it.     After  a  meal,  a  large  part  of  the  blood 
is  sent  to  the  digestive  organs  to  provide  them  with  the 
materials  for  work.     When  one  is  studying,  a  larger  amount 
than  usual  is  sent  to  the  brain.     In  exercise,  the  muscles 
receive  an  increased  supply.     From  these  facts  we  can  under- 
stand why  one  should  not  exercise  vigorously  immediately 
after  a  hearty  meal.     It  also  explains  why  a  light  meal  before 
retiring  may  induce  sleep  by  calling  the  blood  from  the  brain 
to  the  digestive  organs.     The  regulation  of  the  blood  supply  is 
effected  by  nerves  which  cause  the  blood  vessels  to  increase 
or  diminish  in  size.     In  blushing,  the  capillaries  are  dilated  and 
a  larger  amount  of  blood  is  sent  to  the  skin.    Fear  and  some 
other  emotions  cause  the  capillaries  to  contract  and  make  the 
skin  pale.     Heat  also  causes  the  capillaries  to  expand  and  cold 
causes  them  to  contract.     When  injuries  or  the  attacks  of 
bacteria  cause  an  unusual  flow  of  blood  to  any  part,  we  speak 
of  it  as  congestion. 

226.  Bleeding. — If  a  blood  vessel  is  injured,  the  blood,  ow- 
ing to  the  pressure  upon  it,  begins  to  run  out.     If  a  vein_is 


266  EXPERIMENTAL   GENERAL   SCIENCE 

cut  the  flow  will  be  steady,  but  if  an  artery  is  injured,  the  blood 
will  flow  in  jets  corresponding  to  the  heart  beats.  Arterial 
blood  may  also  be  distinguished  from  venous  blood  by  being  a 
brighter  red.  Bleeding  from  small  injuries  is  usually  not  long 
continued.  The  blood  as  it  reaches  the  surface  tends  to 
thicken  and  form  a  clot.  This  is  due  to  the  formation  of 
fibers  of  a  protein  called  fibrin  which  entangle  the  red  cor- 
puscles in  their  meshes.  Slight  injuries  are  best  cleansed 
with  water  and  a  mild  disinfectant  and  wrapped  with  a 
clean  cloth  to  prevent  the  entrance  of  dirt  and  bacteria. 
When  bleeding  is  from  an  artery,  the  clot  may  be  formed  with 
difficulty,  in  which  case  it  may  be  necessary  to  take  up  and  tie 
the  artery.  In  order  to  stop  the  flow  of  blood  temporarily, 
the  artery  may  be  compressed  by  a  tight  bandage  between  the 
heart  and  the  point  of  injury.  If  the  flow  is  from  a  large  vein, 
the  pressure  should  be  applied  on  the  side  of  the  injury  farthest 
from  the  heart. 

Practical  Exercises 

1.  How  many  places  on  the  body  can  you  find  where  the  pulse  may  be 
felt? 


2.  Locate  the  pulse  at  the  base  of  the  thumb  on  the  wrist.     How 
many  times  does  your  heart  beat  a  minute?     Make  three  trials. 

3.  Count  your  pulse  after  running  a  short  distance  or  climbing  one  or 
two  flights  of  stairs.     How  much  has  it  increased? 

4.  After  lying  down  for  a  few  minutes,  count  your  pulse.     How  does 
it  compare  with  the  count  when  standing? 

5.  Run  your  finger  along  the  veins  on  the  inside  of  the  forearm,  press- 
ing the  blood  toward  the  wrist,  and  locate  the  valves  in  them. 

6.  Hold  one  hand  above  your  head  and  the  other  down  by  your  side 
while  you  count  fifty.     Explain  the  difference  noted  in  the  veins  on  the 
back  of  the  hand. 


THE   TRANSPORTING   SYSTEM   OF   THE  BODY         267 

7.  Wind  a  string  tightly  about  the  finger  in  the  direction  of  the  finger 
nail  and  with  a  clean  needle  draw  a  drop  of  blood  from  near  the  nail. 
Examine  with  the  microscope  and  note  both  red  and  white  corpuscles. 

8.  Take  a  living  frog  and,  spreading  its  toes  apart,  examine  the  web  be- 
tween them  with  the  microscope.     Note  the  corpuscles  moving  through 
the  capillaries. 

9.  Account  for  the  red  nose  of  the  hard  drinker. 

10.  Why  is  one  likely  to  feel  sleepy  after  a  hearty  meal? 

11.  Is  a  long  walk  before  breakfast  desirable?    Why? 

12.  Is  a  brisk  walk  before  retiring  desirable?     Why? 


13.  How  does  vigorous  exercise  aid  in  sending  fresh  supplies  of  blood 
to  the  remote  parts  of  the  body? 


14.  Why  does  the  application  of  a  hot  water  bag  or  a  mustard  plaster 
to  the  skin  cause  it  to  become  red? 


16.  Why  must  the  blood  of  a  mechanic  circulate  faster  than  the  blood 
of  a  bookkeeper? 

16.  Why  do  we  need  more  covering  when  we  lie  down? 

17.  How  does  tight  clothing  affect  the  circulation? 

18.  Why  may  soaking  the  feet  in  hot  water  relieve  a  headache? 

19.  How  may  rubbing  the  skin  relieve  an  internal  congestion? 

20.  How  may  massage  affect  the  circulation? 


CHAPTER  XXXVIII 
THE  VENTILATING  SYSTEM  OF  THE  BODY 

227.  Respiration. — In  the  animal  or  plant  body,  energy  is 
secured  by  oxidizing  the  food,  that  is,  by  combining  the  oxygen 
of  the  air  with  the  carbon  contained  in  the  food  (§103,  105). 
Much  of  the  energy  used  in  our  factories  is  derived  in  essen- 
tially the  same  way  by  combining  oxygen  with  the  carbon 
in  coal.     The  oxidation  of  the  food  in  living  things  takes  place 
in  the  cells,  and  the  process  is  quite  different  from  breathing 
which  is  properly  Only  the  inspiration  and  expiration  of  the 
air  by  the  lungs.     All  living  things  respire,  but  many  cannot 
strictly  be  said  to  breathe  since  they  have  neither  lungs  nor 
other  organs  for  the  purpose.     In  the  simplest  animals,  indeed, 
each  cell  obtains  the  necessary  oxygen  for  respiration  from  its 
immediate  surroundings,  but,  in  animal  bodies  consisting  of  a 
multitude  of  cells,  means  must  be  found  for  getting  oxygen 
to  the  more  distant  ones  whose  situation  prevents  their  ob- 
taining it  for  themselves.     Thus  have  arisen  gills,  trachea, 
lungs,  and  a  circulatory  system. 

228.  Organs  of  Breathing. — The  nose,  throat,  trachea  or 
windpipe,  the  bronchial  tubes,  and  the  lungs  are  the  organs  of 
breathing  in  man.     The  transfer  of  gases  between  the  blood 
and  the  air  goes  on  only  in  the  lungs,  and  the  other  organs 
of  breathing,  therefore,  serve  chiefly  to  form  a  passageway 
between  the  lungs  and  the  surface  of  the  body.     The  air  passes 
through  the  nose  into  the  throat  and  is  thereby  warmed, 
moistened,  and,  to  a  large  extent,  freed  from  any  dust  it  may 
contain.     From  the  throat  the  air  enters  the  trachea.     This 
is  a  short  tube  kept  open  by  Oshaped  rings  of  cartilage. 

268 


THE  VENTILATING   SYSTEM   OF   THE  BODY  269 

These  rings  may  be  felt  from  the  outside  of  the  throat  just 
below  the  larynx  or  "  Adam's  apple. "  The  trachea  divides  into 
two  tubes  or  bronchi,  one  of  which  goes  to  each  lung.  In 
the  lungs  the  bronchi  are  divided  into  many  smaller  tubes 
which  finally  end  in  the  air  chambers  of  the  lungs.  The  tra- 
chea, bronchi  and  some  other  parts  of  the  air  passages  are 


FIG.  93. — Human  larynx,  trachea*  bronchi,  and  lungs;  showing  the  ramifica- 
tion of  the  bronchi,  and  the  division  of  the  lungs  into  lobules.  (Brubaker.) 

lined  with  ciliated  cells  whose  whip-like  projections  catch 
any  dust  that  may  be  breathed  in  and  gradually  push  it  toward 
the  throat,  where  it  is  swallowed.  The  esophagus,  the  tube 
through  which  food  reaches  the  stomach,  lies  directly  behind 
the  trachea  and  all  food  therefore  passes  across  the  opening 
from  the  throat  into  the  trachea.  It  is  prevented  from 
getting  into  the  trachea  by  a  spoon-shaped  bridge,  the  epi- 


270  EXPERIMENTAL   GENERAL   SCIENCE 

glottis,  which  shuts  down  over  the  opening  whenever  we  swal- 
low. The  lungs  are  two  pinkish,  spongy  bodies  that  fill  the 
cavity  of  the  chest  with  the  exception  of  the  part  occupied 
by  the  heart.  They  consist  of  an  immense  number  of  tiny 
sacs  with  walls  of  connective  tissue  lined  with  mucous  mem- 
brane. In  the  walls  of  these  sacs  are  a  multitude  of  capillaries 
through  the  walls  of  which  the  blood  gives  up  its  carbon  dioxide 
and  takes  on  a  new  supply  of  oxygen.  The  lungs  are  hung 
loosely  in  the  chest  cavity  and  are  surrounded  by  a  mem- 
brane, the  pleura,  which  is  also  folded  back  to  form  a  lining 
for  the  thorax.  Owing  to  the  pressure  of  the  air  within  them, 
the  lungs  always  fill  all  the  space  in  the  thorax. 

229.  Breathing. — The  act  of  breathing  consists  in  making 
the  thorax  larger  and  thus  allowing  more  air  from  outside  to 
press  in  and  expand  the  lungs,  after  which  the  impure  air  is 
forced  out  by  the  weight  of  the  chest  walls  and  other  parts. 
In  enlarging  the  chest  cavity,  the  diaphragm  which  forms  its 
floor  contracts  and  pressed  downward  on  the  contents  of  the 
abdomen.  At  the  same  time  the  ribs  and  breast-bone  rise. 
In  ordinary  breathing  about  30  cubic  inches  of  air  are  inhaled 
and  exhaled  with  each  breath.  There  is  never  a  complete 
change  of  air  in  the  lungs,  however,  since  the  air  simply  surges 
to  and  fro  with  each  breath,  but  the  rapid  diffusion  of  the  oxy- 
gen it  contains  enables  the  blood  to  secure  sufficient  for  the 
use  of  the  cells.  The  exchange  of  gases  goes  on  continuously 
and  not  merely  at  the  time  the  air  is  taken  in.  We  are  never 
able  to  expel  all  the  air  from  the  lungs.  When  we  have  ex- 
haled as  much  air  as  possible,  there  is  still  left  about  100 
cubic  inches.  By  taking  a  deep  breath,  the  lungs  may  be  made 
to  hold  three  times  this  amount.  There  is  some  difference  in 
the  way  men  and  women  breathe.  Men  use  the  diaphragm  as 
well  as  the  ribs  in  breathing,  but  women  breathe  mostly  by 
elevating  the  ribs,  a  method  which  the  prevailing  styles  of 
dress  often  render  necessary.  The  number  of  times  one 


THE  VENTILATING   SYSTEM    OF   THE  BODY  271 

breathes  a  minute  depends  somewhat  upon  circumstances. 
Young  children  may  breathe  as  often  as  forty  times  a  minute. 
Adults  breathe  from  fifteen  to  eighteen  times  a  minute, 
though  when  violently  exercising  the  number  of  breaths  a 
minute  may  rise  to  sixty  or  seventy.  The  muscles  which 
control  breathing  are  involuntary,  though  by  taking  thought 
we  may  for  a  time  modify  or  even  stop  their  action.  It  is 
impossible  for  one  to  hold  his  breath  for  more  than  a  cer- 
tain time.  After  that  the  involuntary  system  asserts  itself. 
Vigorous  exercise,  calling  for  an  increased  amount  of  oxygen, 
causes  one  to  breathe  faster,  but  if  the  exercise  is  begun  sud- 
denly, we  may  find  ourselves  "out  of  breath,"  because  not  all 
the  lung  cells  are  in  use.  If  the  exercise  is  continued  all  the 
lung  cells  are  soon  brought  into  action  and  we  find  we  have 
our  "second  wind"  and  can  then  exercise  without  becoming 
breathless. 

230.  Ventilation. — The  need  for  an  abundant  supply  of  oxy- 
gen in  the  air  we  breathe  accounts  for  the  attention  that  is 
everywhere  paid  to  ventilation.  Nobody  can  work  or  study 
well  in  an  atmosphere  depleted  of  its  oxygen,  though  when  the 
supply  falls  short  it  is  not  noticed  so  quickly  if  the  air  is  kept 
moving.  Every  effort  should  be  made  to  have  one's  surround- 
ings well  ventilated.  One  should  sleep  with  the  window  open 
at  night,  even  in  the  coldest  weather.  Night  air  is  no  more 
harmful  than  day  air.  Many  people,  by  the  use  of  sleeping 
porches,  now  sleep  in  the  open  air  throughout  the  year. 
Open  air  treatment  is  one  of  the  recognized  methods  of  treat- 
ing tuberculosis  or  consumption.  Those  who  are  compelled 
to  pass  much  of  their  time  indoors  should  manage  to  take 
a  brisk  walk  of  a  mile  or  two  daily.  Next  in  importance  to 
ventilation  is  dust  and  dusting.  A  number  of  diseases  are 
spread  by  dust,  and  dusty  locations  and  occupations  should 
be  avoided  whenever  possible.  In  dusting  a  room  a  feather 
duster  should  never  be  used.  This  simply  stirs  up  the  dust 


272  EXPERIMENTAL   GENERAL   SCIENCE 

and  causes  it  to  settle  in  a  new  place.  Dust  should  be  removed 
with  a  damp  cloth  and  the  cloth  thoroughly  cleaned  before 
using  again. 

231.  The  Voice. — At  the  top  of  the  trachea,  where  it  opens 
into  the  throat,  is  a  roughly  triangular  arrangement  of  car- 
tilage, known  as  the  larynx,  in  which  the  voice  is  produced. 
In  ordinary  breathing,  the  air  passes  through  .the  larynx 
without  noise,  but  when  we  speak  the  edges  of  two  flaps  of 
tissue  within  the  larynx  are  caused  to  approach  each  other 
and  their  vibrations  in  the  current  of  air  as  it  passes  out  of  the 
lungs  produce  the  voice.     The  voice  is  reinforced  by  the  throat 
and  back  part  of  the  head  and  modified  into  speech  by  the 
nose,  lips,  tongue,   and  teeth.     In   childhood,  the  voice  is 
rather  high  pitched  but  as  adult  life  is  approached,  the  larynx 
of  boys  increases  in  size  and  their  voices  become  deeper  and 
heavier  in  consequence. 

232.  Colds. — As  a  result  of  chilling  the  body,  the  blood  may 
be  forced  into  the  mucous  membrane  lining  the  organs   of 
breathing  and  there  cause  an  increased  production  of  mucus 
with  its  attendant  coughing  and  spitting.     One  should  avoid 
drafts,  wet  feet,  and  insufficient  clothing  if  one  would  escape 
colds.     While  an  ordinary  cold  may  only  cause  temporary 
discomfort,   the   inflamed   membranes   which   accompany   it 
are  favorite  breeding  places  of  various  germ  diseases  such  as 
diphtheria,  pneumonia,  bronchitis,  and  tuberculosis.     A  few 
colds,  especially  that  form  known  as  a  cold  in  the  head,  are 
caused  by  germs.     One  may  often  save  himself  several  days 
of  illness  by  avoiding  the  vicinity  of  those  who  are  coughing, 
spitting,  and  sneezing.     The  best  remedy  for  the  ordinary  cold 
is  rest  and  an  even  temperature. 

233.  Expression  of  the  Feelings. — The  organs  of  breathing 
are  also  concerned  in  a  number  of  actions  which  express  our 
feelings  or  show  the  condition  of  our  bodies.    Laughing  and 
crying  are  much  alike  and  are  both  produced  by  short  sharp 


THE  VENTILATING   SYSTEM   OF  THE  BODY  273 

motions  of  the  diaphragm.  Sighing  is  a  prolonged  inspiration 
and  expiration  which  appears  to  be  intended  to  increase  the 
supply  of  oxygen  in  the  lungs  when  for  any  reason  we  have 
neglected  to  breathe  deepty  enough.  Yawning  is  much  like 
sighing  except  that  the  air  is  inspired  through  the  mouth.  It 
seldom  occurs  unless  we  are  fatigued.  Snoring  occurs  during 
sleep  when  the  mouth  is  open  and  the  soft  palate  vibrates  in 
the  divided  currents  of  air.  Hiccough  is  due  to  a  strong  spas- 
modic contraction  of  the  diaphragm.  In  coughing  and  sneez- 
ing the  diaphragm  forcibly  expels  air  through  the  mouth. 
The  stimulation  which  causes  coughing  originates  in  the  throat, 
trachea  or  lungs;  in  sneezing,  it  originates  in  the  nose.  Most 
actions  of  this  kind  are  reflex. 

Practical  Exercises 

1.  How  many  times  do  you  breathe  a  minute  while  sitting?     Make 
three  trials. 

2.  Count  the  number  of  times  you  breathe  a  minute  after  running  a 
hundred  feet  or  climbing  two  flights  of  stairs. 

3.  How  many  times  does  your  heart  beat  while  you  are  breathing  once  ? 

4.  Expel  as  much  breath  as  possible  and  measure  the  circumference 
of  the  thorax,  passing  the  tape  around  it  just  beneath  the  arms.     Then 
take  as  long  a  breath  as  possible  and  measure  again.     How  many  inches 
can  you  expand? 

6.  Get  a  bottle  holding  three  or  four  quarts,  fill  it  with  water  and 
invert  in  a  large  pan  of  water.  Keeping  the  mouth  of  the  bottle  under 
water,  by  means  of  a  rubber  tube  blow  into  the  bottle  as  much  air  as 
possible  with  one  breath.  Try  the  experiment  with  a  tight  band  around 
the  waist.  Explain  the  difference. 

6.  Speak  the  vowels.     Do  you  make  these  sounds  with  the  mouth 
open  or  shut? 
18 


274  EXPERIMENTAL   GENERAL   SCIENCE 

7.  What  parts  of  the  mouth  do  you  use  in  pronouncing  the  consonants 
m,  b  and  p? 

8.  What  parts  are  used  in  pronouncing  the  consonants  t,  d  and  s? 

9.  What  disadvantage  is  there  in  breathing  through  the  mouth? 

10.  Why  is  one  likely  to  take  short  breaths  after  a  hearty  meal? 

11.  Why  is  the  guest  chamber  often  unhealthful? 

12.  Which  has  the  best  ventilation,  your  church,  your  schoolroom,  or 
your  home? 

13.  Is  your  favorite  moving  picture  house  properly  ventilated? 

14.  Why  is  it  better  to  have  clothing  hang  from  the  shoulders  than 
from  the  waist? 


CHAPTER  XXXIX 
THE  COVERING  OF  THE  BODY 

234.  The  Skin. — The  delicate  and  sensitive  tissues  of  the 
body  are  everywhere  covered  with  a  protective  layer  called 
the  skin.     Not  only  is  the  entire  surface  of  the  body  thus  pro- 
tected, but  the  mucous  and  serous  membranes,  the  first  named 
lining  all  the  passages  of  the  interior  to  which  air  has  access, 
and  the  serous  membrane  lining  the  closed  cavities,  are  essen- 
tially modified   skin.     Even   the   teeth,   the  hardest  struc- 
tures in  the  body,  are  modifications  of  this  tissue,  as  are  also 
the  hair  and  the  nails.     The  most  important  function  of  the 
skin  is  to  protect  the  body  from  germs  and  mechanical  injury, 
but  it  also  aids  in  excretion  and  in  regulating  the  temperature 
of  the  body.     Certain  of  the  special  senses  are  also  located  in 
the  skin. 

235.  Structure  of  the  Epidermis. — There  are  two  layers  of 
the  skin  known  usually  as  the  epidermis  or  cuticle  and  the 
dermis,  respectively.     The  epidermis  is  on  the  outside  and  con- 
sists of  many  layers  of  cells,  flattened  near  the  surface  and 
more  rounded  deeper  in  the  tissue.     It  has  neither  blood  ves- 
sels nor  nerves,  and  derives  its  materials  for  growth  and  repair 
from  the  dermis.     It  is  constantly  wearing  out,  as  may  be 
inferred  from  the  rapidity  with  which  a  stain  disappears  from 
it,  and  is  as  constantly  renewed  by  the  living  cells  in  contact 
with  the  dermis.     The  epidermis  varies  in  thickness  on  various 
parts  of  the  body,  being  thickest  on  the  palms  of  the  hands  and 
the  soles  of  the  feet.     It  may  become  thicker  elsewhere  when 
an  unusual  amount  of  wear  is  brought  upon  it.     Corns  and 
callouses  are  due  to  the  attempts  of  the  epidermis  to  protect 

275 


276  EXPERIMENTAL   GENERAL   SCIENCE 

the  tissues  beneath  by  an  extra  pad  of  its  substance.  When 
we  make  a  blister,  it  is  the  epidermis  which  is  pushed  out  by 
the  accumulation  of  lymph  beneath  it.  The  deeper  parts  of 
the  epidermis  contain  varying  amounts  of  pigment  whose 
relative  abundance  makes  the  difference  between  blondes  and 
brunettes.  Exposure  to  the  sun  or  wind  causes  more  of  the 
pigment  to  develop.  If  this  is  spread  in  an  even  layer  we  call 
it  tan;  if  it  occurs  in  spots  it  forms  freckles.  The  negro's 
skin  is  dark  because  of  a  superabundance  of  this  pigment. 
Occasionally  an  individual  is  found  who  entirely  lacks  pigment. 
Such  a  person  is  called  an  albino. 

236.  The  Dennis. — The  dermis  or  true  skin  is  made  up  of 
connective  tissue  and  is  richly  supplied  with  blood  vessels  and 
nerves.     It  is  loosely  connected  to  the  muscles  beneath  and 
moves  smoothly  over  them.     It  is  this  tissue  in  animals  that 
is  tanned  to  make  leather.    At  the  point  where  the  dermis 
is  in  contact  with  the  epidermis,  that  is,  on  its  outer  surface, 
it  is  thrown  up  into  small  projections  called   papilla.     Warts 
are  merely  overgrown    papillae.     The  papillae  are    set  very 
regularly  on  the  palms  of  the  hands  and  the  finger  tips  and 
this  produces  the  fine  lines  or  ridges  with  which  everybody 
is  familiar.     The  lower  layers  of  the  dermis  are  often  used  by 
the  body  for  the  storage  of  fat.     This  is  especially  noticeable 
in  the  region  over  the  abdomen. 

237.  Outgrowths  of  the  Skin. — With  the  exception  of  the 
palms  of  the  hands  and  the  soles  of  the  feet,  the  skin  is  covered 
with  fine  hairs.    These  hairs  are  each  set  in  a  depression  of  the 
dermis  and  are  supplied  with  blood  vessels,  nerves,  and  muscles. 
Hairs  are  really  tubes  of  the  same  tissue  that  forms  the  epi- 
dermis.    They  grow  from  small  elevations  called  hair  follicles. 
If  a  hair  be  pulled  out,  another  will  grow  in  its  stead  provided 
the  follicle  is  not  injured.     The  hair,  itself,  contains  neither 
nerves  nor  blood  vessels  though  these  occur  in  the  follicles. 
When  the  skin  is  chilled,  the  muscles  at  the  base  of  the  hairs 


THE  COVERING  OF  THE  BODY          277 

attempt  to  make  them  stand  erect,  as  the  hairs  of  the  lower 
animals  do  in  cold  weather.  This  causes  the  condition  known 
as  "gooseflesh."  The  difference  between  straight  and  curly 
hair  is  due  to  a  difference  in  the  shape  of  the  hair  itself.  Curly 
hair  is  flattened;  straight  hair  is  cylindrical.  When  hair  is 
artificially  curled  it  is  temporarily  flattened  in  various  ways. 
The  nails  are  also  modifications  of  the  epidermis,  designed  to 
protect  the  finger  tips  and  assist  in  picking  up  small  objects. 
They  are  set  in  grooves  of  the  epidermis  and  grow  in  length 
from  the  base  and  in  thickness  from  the  under  side.  Being 
semi-transparent  they  appear  pink  from  the  reflection  of  the 
blood  beneath  them.  In  the  lower  animals,  claws,  horns, 
beaks,  feathers,  tortoise-shell,  and  various  other  structures 
are  derived  from  the  skin. 

238.  Glands  of  the  Skin. — At  the  base  of  the  hairs  and  in 
other  parts  of  the  skin  are  certain  tiny  glands  which  pour  out 
an  oil  that  keeps  the  hairs  soft  and  the  skin  flexible.     These 
are  called  sebaceous  glands.     The  sebaceous  glands  of  the  face 
sometimes  become  clogged  with  dirt  and  are  then  known  as 
"blackheads."     More  noticeable  are  the  sweat  glands  which 
give  off  much  water  when  the  bodily  temperature  rises  above 
a  certain  point.     Though  the  perspiration  is  noticed  only 
when  the  body  is  warm,  we  perspire  more  or  less  constantly 
even  in  winter.     This  may  be  seen  by  touching  a  cold  mirror 
or  piece  of  metal  when  a  thin  film  of  moisture  will  appear. 
The  sweat  glands  begin  in  the  lower  layers  of  the  dermis  as 
coiled  tubes  closed  at  the  ends.     The  water  and  salt  they 
excrete  are  taken  from  the  blood  like  the  material  used  by 
other  glands.     With  a  good  lens,  the  openings  of  the  sweat 
glands  may  be  seen  in  the  ridges  on  the  finger  tips.     If  the 
hands  are  warm,  a  slight  pressure  will  cause  minute  drops  of 
perspiration  to  appear  from  the  openings. 

239.  Functions  of  the  Perspiration. — Since  the  heat  of  the 
body  is  derived  from  the  oxidation  of  the  food,  its  production 


278  EXPERIMENTAL   GENERAL   SCIENCE 

is  continuous  and  the  surplus  must  be  as  continuously  thrown 
off,  otherwise  the  body  would  soon  reach  a  temperature  high 
enough  to  cause  the  death  of  the  tissues.  Fever  is  simply 
the  excess  heat  which  remains  in  the  body  under  certain  con- 
ditions. When  the  atmosphere  is  cool,  most  of  the  surplus 
heat  is  lost  by  radiation  (§77).  In  winter  it  is  necessary  to 
put  on  additional  clothing  to  prevent  too  rapid  radiation  of 
the  heat,  but  in  summer,  when  the  temperature  of  the  air  is 
high,  mere  radiation  is  not  sufficient  and  the  nerves  stimulate 
the  sweat  glands  to  pour  out  a  large  amount  of  perspiration 
which,  evaporating,  takes  much  heat  from  the  body  (§92). 
By  this  means  the  bodily  temperature  is  kept  uniform.  The 
average  temperature  of  the  human  body  is  98.6°  F.  but  the 
skin  is  usually  somewhat  cooler  and  some  parts  of  the  body, 
notably  the  liver,  is  several  degrees  warmer.  Certain  drugs, 
by  affecting  the  nerves,  may  also  promote  the  pouring  out 
of  the  perspiration.  Since  the  air  taken  into  the  lungs  is 
warmed  during  its  journey  through  the  air  passages,  a 
considerable  amount  of  heat  is  also  lost  in  breathing. 

240.  Care  of  the  Skin. — The  skin  should  be  washed  often 
enough  to  keep  it  free  from  the  dirt  and  germs  with  which  it 
comes  in  contact,  as  well  as  to  rid  it  of  the  secretions  left 
behind  when  the  perspiration  evaporates.  A  bath  at  least 
once  a  week  is  desirable.  Daily  bathing,  while  not  absolutely 
necessary,  is  valuable  for  its  beneficial  effects  upon  the  skin. 
Sufficient  clothing  should  be  worn  at  all  times  to  protect  the 
body  from  being  chilled,  but  an  unusual  amount  of  clothes 
for  wear  in  the  house  in  winter  is  likely  to  prove  harmful. 
It  is  much  better  to  add  extra  wraps  when  going  out  into  the 
cold  than  to  dress  too  warmly  indoors.  Nor  is  it  desirable 
that  the  temperature  of  the  living  rooms  be  high  in  winter. 
A  temperature  of  68°F.  or  70°F.  is  the  proper  one.  Since  the 
evaporation  of  the  perspiration  depends  upon  the  amount  of 
moisture  in^the  air,  being  greatest  when  the  humidity  is  low, 


THE  COVERING  OF  THE  BODY          279 

merely  increasing  the  amount  of  moisture  in  the  air  may 
make  the  surroundings  seem  warmer.  The  relative  humidity 
in  our  dwellings  and  school  rooms  should  be  about  50  per 
cent.  (§94). 

Practical  Exercises 

1.  Lift  the  skin  on  the  back  of  the  hand.     How  thick  is  it? 

2.  How  may  drinking  ice-water  cool  the  body? 

3.  Is  it  desirable  to  take  a  hot  bath  immediately  after  a  hearty  meal? 
Why? 

4.  If  one  ties  a  string  tightly  about  his  finger,  it  soon  becomes  cold. 
Why? 

6.  Why  does  wet  clothing  make  the  body  feel  chilly  (§92)? 

6.  Why  can  a  fat  man  endure  cold  better  than  a  thin  one? 

7.  In  summer  why  does  it  seem  so  oppressive  when  the  air  is  moist 
(§94)? 

1 

8.  Why  may  rubbing  the  skin  when  the  body  is  chilled  prevent  one 
from  taking  cold? 

9.  Touch  the  tips  of  the  hairs  on  the  back  of  your  hand.     What  indica- 
tion does  this  give  that  the  hair  follicle  is  supplied  with  a  nerve? 

10.  The  finger  prints  of  no  two  persons  seem  to  be  alike.     Smear  your 
thumb  or  finger  tip  with  ink  and  make  a  clear  ringer  print  of  your  own. 
Compare  it  with  that  of  your  classmates. 

11.  Draw  a  hair  between  your  thumb  and  finger  nail,  pressing  firmly 
upon  it,  and  explain  the  behavior  of  the  hair  when  released. 


CHAPTER  XL 
THE  EXCRETION  OF  WASTE  FROM  THE  BODY 

241.  Need  for  Excretion. — So  long  as  the  body  is  alive  it 
needs  a  steady  supply  of  food,  partly  to  build  up  new  tissues 
and  to  repair  worn  ones,  and  partly  to  supply  the  energy  by 
means  of  which  the  tissues  are  able  to  work.  Ultimately, 
through  wear  or  oxidation,  the  materials  of  the  body  break 
down  into  substances  that  are  not  only  useless  but  harmful, 
and  these  wastes  are  thrown  out  by  the  organs  of  excretion. 
When  carbohydrates  and  fats  are  oxidized  in  the  body,  they 
return  to  the  elements  from  which  they  were  made — carbon 
dioxide  and  water.  Most  of  this  carbon  dioxide  and  part 
of  the  water  are  given  off  through  the  lungs.  These  organs, 
in  addition  to  their  function  of  supplying  oxygen  to  the 
body,  are  thus  seen  to  be  true  organs  of  excretion.  A  small 
amount  of  carbon  dioxide  and  a  much  greater  amount  of 
water  are  excreted  by  the  skin,  and  this  organ  also  excretes 
some  salt  and  urea,  the  latter  a  waste  from  the  nitrogenous 
part  of  the  food.  The  liver  is  seldom  thought  of  as  an  organ 
of  excretion,  though  the  bile,  useful  as  it  is  in  digestion,  con- 
tains much  waste  matter  which,  poured  into  the  small  intes- 
tine, passes  out  of  the  body  with  the  refuse  from  the  food. 
The  liver  also  builds  up  certain  substances  from  the  waste 
matters  in  the  blood  which  are  returned  to  the  blood  to  be 
later  excreted  by  the  kidneys.  These  latter  are  the  principal 
organs  for  the  elimination  of  protein  wastes  from  the  body  and 
also  share  with  the  skin  the  duty  of  disposing  of  the  excess 
water  absorbed. 

280 


THE  EXCRETION  OF  WASTE  FROM  THE  BODY   281 

242.  The  Kidneys.— The  kidneys  are  two  dark  red,  bean- 
shaped  organs,  somewhat  smaller  than  the  fist,  which  lie  on 
either  side  of  the  spinal  column  just  below  the  ribs.  Through 
the  many  capillaries  of  the  kidneys,  all  the  blood  of  the  body 
sooner  or  later  passes  and  these  organs  are  therefore  able  to 
select  and  remove  the  wastes  it  contains.  The  actual  work 


Renal  vei 


FIG.  94. — Posterior  view  of  the  right  kidney.     (Morris.) 


of  excretion  is  performed  by  the  glandular  cells  of  many  small 
tubes,  not  unlike  sweat  glands  in  structure,  which  make 
up  the  bulk  of  the  kidneys.  The  material  excreted  is  not 
merely  strained  out  of  the  blood.  The  action  is  a  true  excre- 
tion in  which  the  materials  are  selected  by  the  cells  much  as 
other  glandular  cells  produce  their  characteristic  substances. 
Some  of  the  substances  excreted  by  the  kidneys,  however, 


282  EXPERIMENTAL   GENERAL   SCIENCE 

appear  to  be  formed  in  the  liver  and  left  for  the  kidneys  to 
remove  from  the  blood.  The  most  abundant  substance 
excreted  by  the  kidneys  is  of  course  water,  but  with  it  are 
excreted  salt,  urea,  and  other  substances  which  are  dissolved 
in  it.  A  single  tube,  the  ureter,  leads  from  each  kidney  to  the 
bladder  where  the  material  is  stored  until  expelled  from  the 
body.  The  ureter  leaves  the  kidney  from  the  concave  side 
and  here  also  enters  and  leaves  the  blood  supply  to  these 
organs.  The  refuse  from  the  food  taken  into  the  alimentary 
canal  cannot  properly  be  considered  an  excretion.  Its  reten- 
tion in  the  body,  however,  may  be  as  harmful  as  the  reten- 
tion of  any  of  the  substances  ordinarily  excreted,  since  it 
forms  an  ideal  breeding  place  for  bacteria  which  of  themselves 
may  produce  poisons  very  harmful  when  absorbed. 

243.  Conditions  Affecting  Excretion. — When  the  kidneys 
function  properly,  the  nitrogenous  waste  is  excreted  as  fast  as 
made  in  the  body,  but  the  amount  of  water  excreted  depends 
somewhat  upon  the  temperature  to  which  the  body  is  sub- 
jected, the  amount  of  moisture  in  the  air,  and  sometimes  on 
the  condition  of  the  nervous  system.  In  warm  weather,  a 
large  part  of  the  water  taken  into  the  body  is  evaporated 
from  the  skin  as  perspiration,  but  in  winter  a  larger  propor- 
tion is  excreted  by  way  of  the  kidneys.  Since  meats  and  other 
nitrogenous  foods  result  in  wastes  that  must  be  eliminated  by 
the  kidneys,  those  suffering  from  diseases  of  these  organs 
find  it  desirable  to  greatly  reduce  the  proteins  in  their  diet. 
Since  the  salts  and  other  wastes  excreted  by  the  kidneys  are 
dissolved  in  water,  the  need  for  drinking  sufficient  water  to 
keep  the  kidneys  flushed  out  is  apparent. 

Practical  Exercises 

1.  Why  do  people  suffering  from  kidney  trouble  find  a  warm  climate 
desirable? 


THE  EXCRETION  OF  WASTE  FROM  THE  BODY   283 

2.  How  may  sufficient  clothing  relieve  the  kidneys  of  part  of  their 
work? 


3.  On  a  hot  day  we  may  drink  much  water  without  increasing  the 
excretions  from  the  kidneys.     Why? 

4.  Why  does  vigorous  exercise  cause  more  carbon  dioxide  to  be  given 
off  by  the  breath? 


CHAPTER  XLI 

THE  SPECIAL  SENSES 

244.  Function  of  Sensations. — The  greater  part  of  our 
tissues  seem  designed  simply  for  the  purpose  of  maintaining 
the  body  as  a  living  and  healthy  organism.  The  alimentary 
canal  serves  for  the  digestion  of  food,  the  blood  to  carry  the 
digested  food  to  the  cells,  the  lungs  to  obtain  oxygen  by  means 
of  which  the  muscles  can  release  the  energy  in  the  food,  and 
the  organs  of  excretion  for  the  disposal  of  the  wastes.  All 
these  functions  are  characteristic  of  living  things  in  general 
and  proceed  automatically  without  the  organism  taking 
thought  of  the  matter;  indeed  many  of  the  bodily  processes 
appear  to  go  on  as  well  when  we  are  asleep  as  when  we  are 
awake.  There  is,  however,  another  faculty  developed  in  the 
body  which  we  term  consciousness  and  by  means  of  which  we 
are  made  aware  of  our  surroundings  and  are  thus  able  to 
enjoy  existence.  This  faculty  is  located  in  the  cerebrum 
which  forms  the  upper  and  forward  part  of  the  brain,  It 
communicates  with  the  outer  world  through  the  nerves  and 
end  organs,  the  latter  located  at  various  places  on  the  exterior 
of  the  body.  The  end  organs,  however,  serve  merely  to  re- 
ceive and  transmit  sensations  and  have  no  part  in  the  appre- 
ciation of  such  sensations.  This  latter  is  a  function  of  the 
cerebrum  alone.  Some  of  the  sensations  coming  to  the  brain 
have  no  definite  sense  organs  for  their  perception  and  they  are 
therefore  called  general  sensations.  In  this  group  may  be 
included,  hunger,  pain,  thirst,  fatigue,  satiety  and  various 
others  concerned  in  the  upkeep  of  the  body.  Impressions 
from  the  external  world,  however,  are  all  perceived  by  special 

284 


THE    SPECIAL   SENSES  285 

sense  organs  each  designed  to  perceive  its  special  kind  of  sen- 
sation and  is  incapable  of  reporting  any  other. 

246.  The  Special  Senses. — Several  of  the  organs  of  special 
sense  do  not  have  to  come  in  contact  with  what  they  report 
upon  to  be  affected  by  them.  By  the  sense  of  sight,  the  eye 
perceives,  often  at  considerable  distances,  sizes,  colors,  shapes 
and  motions  and  by  the  sense  of  hearing,  the  ear  detects  vibra- 
tions in  other  bodies.  The  sense  of  smell  enables  the  nose  to 
judge  of  the  odors  of  substances  at  a  distance,  though  in  this 
case  particles  of  the  substance  in  a  finely  divided  condition  or 
in  the  gaseous  form  must  enter  the  nose  and  come  in  contact 
with  the  sense  organs.  By  the  sense  of  taste,  the  tongue  judges 
of  the  flavors  of -different  substances,  though  this  sense  is  not 
as  comprehensive  as  we  often  imagine  it  to  be,  for  much  of 
what  passes  for  taste  is  really  due  to  sensations  sent  to  the 
brain  by  the  nose.  To  be  tasted,  substances  have  to  be  dis- 
solved. The  sense  of  touch  is  the  most  widely  distributed  of 
all  the  special  senses,  being  located  throughout  the  skin  and  in 
many  parts  of  the  mucous  membrane  as  well.  It  is  probably 
the  sense  from  which  all  the  others  have  been  derived.  The 
five  special  senses  are  commonly  supposed  to  be  all  that  the 
body  possesses,  but  it  can  be  easily  shown  that  there  is  a  tem- 
perature sense  in  the  skin  by  means  of  which  we  are  able  to 
ascertain  whether  a  thing  is  hotter  or  colder  than  the  skin 
itself,  and  an  equilibrium,  sense  in  the  ear  which  keeps  the  body 
informed  of  its  position  in  space. 

246.  The  End  Organs  of  Special  Sense.— The  end  organs  of 
special  sense,  each  responding  to  its  appropriate  stimuli,  are 
necessarily  modified  for  the  duties  they  have  to  perform. 
Those  which  are  concerned  with  touch  and  temperature  are 
found  in  papillae  very  much  like  the  other  papillae  of  the 
dermis.  Those  which  receive  sensations  of  touch  are  some- 
what unevenly  distributed,  being  most  numerous  on  the  tip  of 
the  tongue,  the  lips,  finger  tips  and  forehead,  and  farthest 


286  EXPERIMENTAL   GENERAL   SCIENCE 

apart  on  the  small  of  the  back.  The  end  organs  which  per- 
ceive differences  in  temperature  are  scarcely  to  be  distinguished 
from  those  of  touch,  though  they  react  to  a  different  set  of 
stimuli.  The  organs  of  smell  come  to  the  surface  in  the 
mucous  membrane  in  the  upper  part  of  the  nose,  and  are  very 
similar  to  ordinary  cells  surrounding  them.  They  are  so 
located  that  they  can  perceive  odors  in  the  air  currents  as 
they  pass  into  the  body  and  thus  notify  us  when  the  sur- 
rounding air  is  losing  its  purity.  The  sense  of  smell  is  very 
easily  tired  and,  after  reporting  an  odor  for  a  short  time,  ceases 
to  be  stimulated  by  it.  This  accounts  for  the  fact  that  people 
who  work  with  ill-smelling  materials  soon  cease  to  be  annoyed 
by  the  odors.  Though  the  sense  of  smell  is  easily  fatigued, 
the  impressions  made  by  smells  on  the  memory  are  very  lasting, 
and  the  sense  itself  is  exceedingly  keen.  One  part  of  vanilla 
in  eight  million  parts  of  air  can  be  detected  by  this  sense. 
The  sense  of  taste  is  located  in  certain  taste  buds,  mostly  on 
the  upper  surface  of  the  tongue.  There  are  three  forms  of 
these  taste  buds;  those  on  the  back  of  the  tongue  are  relatively 
few  in  number  and  consist  of  elevations  each  surrounded 
by  a  circular  depression;  those  on  the  rest  of  the  tongue  are 
either  thread-like  bodies  embedded  in  the  other  cells  or  are 
mushroom-like  structures  scattered  here  and  there.  These 
latter  may  be  clearly  seen  with  the  unaided  eye.  The  tip  of 
the  tongue  best  perceives  sweets,  the  sides  are  most  affected  by 
acids,  and  those  at  the  back  of  the  tongue  by  bitter  substances. 
These  three  classes  of  flavors  are  all  that  the  tongue  really 
perceives,  as  may  be  easily  seen  by  holding  the  nose  while 
testing  other  substances.  Great  heat  and  cold  paralyze  the 
sense  of  taste. 

247.  Sight  and  Hearing. — Sight  and  hearing,  concerned 
with  vibrations  in  the  ether  and  vibrations  in  the  air  re- 
spectively, have  much  more  complicated  organs  for  receiving 
impressions  than  have  those  of  the  other  senses.  The  organs 


THE    SPECIAL   SENSES 


287 


of  hearing  are  located  in  a  bony  chamber,  half  the  size  of  the 
finger  tip,  in  each  side  of  the  head.  This  chamber  is  filled 
with  a  fluid  into  which  certain  delicate  filaments  from  the 
nerves  project,  and,  when  the  fluid  is  caused  to  vibrate,  the 
filaments  transmit  sensations  of  sound  to  the  brain.  A  narrow 
passage  leads  from  the  outside  to  this  chamber  and  at  its  inner 
end  is  closed  by  a  membrane  commonly  known  as  the  ear 
drum.  When  vibrations  fall  on  the  ear  drum,  three  tiny  bones 
carry  them  across  the  short 
space  between  the  ear  drum 
and  the  bony  chamber  and 
cause  vibrations  in  its  con- 
tents. A  tiny  tube,  the 
eustachian  tube,  leads  from 
the  throat  to  the  inner  side 
of  each  ear  drum  and  serves 
to  equalize  the  pressure  of 
the  air  on  the  two  sides  of 
the  membrane.  The  eyes, 
the  only  two  parts  of  the 
body  that  are  sensitive  to 
light  rays,  function  like  a  set 
of  lenses  to  focus  the  light  on 
an  inner  sensitive  part,  the 
retina,  from  which  sensations  of  sight  go  to  the  brain.  The 
interior  of  the  eye  is  lined  with  a  tissue  containing  pigment 
which  absorbs  such  light  rays  as  do  not  fall  upon  the  retina. 
In  the  front  of  the  eye,  this  pigment  is  visible  and  forms  the 
iris.  The  dark  spot  or  pupil  of  the  eye  is  really  an  opening 
through  the  iris,  and  the  iris  itself  is  able  to  contract  or  expand 
and  thus  modify  the  amount  of  light  admitted.  Behind  the 
iris,  an  organ  called  the  crystalline  lens  aids  in  focussing  the 
light  rays.  It  is  unable  to  move  forward  and  back  as  camera 
lenses  do,  but  accomplishes  the  same  end  by  becoming  thicker 


FIG.  95.— The  ear. 


288 


EXPEETMENTAL   GENERAL   SCIENCE 


or  thinner  and  thus  changing  its  curvature.  The  eye,  being 
one  of  the  most  delicate  parts  of  the  body,  is  appropriately 
protected  by  a  bony  socket,  eyelids  and  projecting  eyebrows. 
On  the  upper  and  outer  side  of  the  eye,  is  a  tear  gland  which 
supplies  a  watery  fluid  that  serves  to  keep  the  eye  moist 
and  free  from  dust.  When  one  is  under  strong  emotion,  or 
when  the  eye  is  irritated,  the  tear  glands  pour  out  an  extra 
amount  of  fluid  which  gathers  in  drops  and  overflows  upon 


Retina 


Cornea 


-  Ciliary  processes 

Lymph  canal 
Ciliary  muscle 


FIG.  96. — A  section  of  the  eye.     (Holden.} 

the  cheeks.     Ordinarily  the  surplus  moisture  is  drained  away 
through  a  tiny  tube  into  the  nose. 

Practical  Exercises 

1.  Why  do  we  sniff  when  we  are  attempting  to  locate  a  faint  odor? 

2.  Why  does  one  smack  his  lips  when  carefully  tasting  a  substance? 

3.  Why  may  a  substance  first  taste  sweet  and  then  bitter? 


THE    SPECIAL   SENSES  289 

4.  After  a  spell  of  crying,  why  does  the  nose  need  attention? 

HI" 

j    5.  Why  may  a  cold  in  the  head  cause  our  food  to  lose  its  flavor? 


6.  Why  has  sand  no  taste? 

)r~ 

i  _ 

7.  How  does  holding  the  nose  keep  one  from  tasting  nauseous  medi- 
ines? 


8.  Wipe  the  tongue  dry  and  put  some  sugar  on  it.     Can  you  taste  it? 
Why? 


9.  Of  what  special  advantage  is  there  in  the  nose  being  above  the 
mouth? 


10.  Why  may  the  smell  of  a  good  dinner  make  a  hungry  man's  mouth 
water? 


11.  Why  can  you  hear  the  ticking  of  a  watch  more  distinctly  when  you 
close  your  teeth  upon  it? 


12.  Why  may  a  cold  cause  one  to  hear  less  distinctly? 

13.  Can  the  special  senses  be  educated? 

14.  Why  do  near  sighted  people  without  glasses  bring  their  work  so 
close  to  their  eyes? 

15.  Why  do  people  listening  to  a  faint  sound,  open  their  mouths? 

16.  Why  do  people  put  the  open  hand  behind  their  ear  when  trying  to 
catch  faint  sounds? 

19 


290 


EXPERIMENTAL   GENERAL   SCIENCE 


17.  Have  a  classmate  touch  the  back  of  your  hand,  cheek,  finger  tips, 
etc.,  with  the  points  of  a  pair  of  compasses.  Where  can  you  distinguish 
the  two  points  when  closest  together? 


18.  Draw  a  thin  piece  of  ice  slowly  across  the  back  of  the  hand  and 
mark  with  a  pencil  the  points  where  cold  is  felt.  Make  the  same  experi- 
ment with  a  wire  dipped  in  hot  water.  Does  the  same  point  perceive 
both  heat  and  cold? 


19.  Why  is  it  difficult  to  detect  the  flavor  of  hot  food? 


CHAPTER  XLII 
THE  EFFECT  OF  DRUGS  ON  THE  BODY 

248.  Drugs. — Although  plants,  or  substances  derived  from 
plants,  make  up  the  bulk  of  our  food,  there  are,  nevertheless, 
many  plants  in  the  world  which  react  in  a  harmful  way  with  the 
protoplasm  of  the  body.     Even  mustard,  which  is  used  in 
small  quantities  with  the  food  as  a  condiment,  when  applied 
in  larger  amounts  to  the  skin  will  form  blisters.     Contact 
with  poison  ivy  or  poison  sumach  may  also  cause  the  skin  to 
blister,  accompanied  by  an  intolerable  itching.     The  common 
nettle,  if  lightly  touched,  will  sting  the  hand  with  almost  the 
intensity  of  a  bee  sting.     Fortunately  there  are  very  few  plants 
in  the  United  States  that  act  as  contact  poisons,  but  there  are 
a  great  many  of  even  our  common  plants  that  will  cause  death 
if  eaten.     Most  of  these  plants  are  harmful  because  of  an 
alkaloid  they  contain,  but  the  fact  that  the  alkaloids  strongly 
affect  different  parts  of  the  body  may  be  taken  advantage  of 
in  medicine.     In  the  hands  of  a  skilful  physician  even  the 
most  deadly  may  be  used  in  the  cure  of  disease.     The  plants 
and  plant  products  used  in  medicine  are  called  drugs.     In 
the  case  of  most  drugs,  however,  it  is  not  the  drugs  themselves 
which  cause  the  cure  but  rather  the  nervous  system  which  is 
stimulated  by  the  drugs  to  cause  a  greater  activity  in  the  cells. 
It  is  sometimes  a  question  whether  drugs  are  really  of  use  in 
illness,  and  the  physician  is  coming  more  and  more  to  rely  upon 
rest,  a  proper  diet,  and  careful  nursing  for  the  recovery  of  his 
patient. 

249.  Use  of  Drugs. — Although  the  physician  may  prescribe 
drugs  to  be  taken  during  illness,  when  we  recover  our  health, 
we  are  in  no  need  of  drugs.     Nevertheless,  in  almost  every 
land,  man  has  shown  a  disposition  to  make  use  of  certain  sub- 
stances of  this  kind.     Those  he  most  favors  are  such  as  give 

201 


292  EXPERIMENTAL   GENERAL   SCIENCE 

him  a  pleasurable  feeling  of  restfulness  and  bodily  comfort 
by  partially  stupefying  the  nervous  system.  Such  drugs  are 
called  narcotics.  Other  narcotics  may  first  act  as  stimulants 
and,  by  driving  the  cells  of  the  body  at  a  faster  pace  than 
normal,  produce  a  feeling  of  ease  and  lightness  of  spirits  which 
some  people  find  attractive.  Sooner  or  later,  however,  there 
comes  a  reaction  in  which  the  body  pays  for  its  past  excesses 
by  a  feeling  of  dullness  and  depression  until  the  person  again 
partakes  of  the  drug  which  renews  the  feeling  of  pleasurable 
elation.  When  once  the  use  of  such  substances  is  begun, 
however,  a  craving  is  soon  developed  which  can  only  be  satis- 
fied with  new  and  often  larger  amounts  of  the  same  substance, 
and  thus  a  habit  is  formed  which  is  difficult  or  practically 
impossible  to  break.  The  commonest  of  the  drugs  containing 
alkaloids  used  by  man  are  tea,  coffee,  cocoa,  chocolate,  opium, 
morphine,  cocaine  and  tobacco.  Of  these,  opium,  morphine, 
and  cocaine  are  such  harmful  drugs  that  their  sale  to  persons 
other  than  physicians  is  wisely  forbidden  by  law  in  most  States. 

250.  Tea,  Coffee  and  Other  Beverages. — Tea,  coffee,  cocoa, 
and  chocolate  are  almost  universally  used  as  beverages  and 
in  the  quantities  ordinarily  taken  seldom  cause  harm,  though 
all  contain 'alkaloids  very  similar  in  their  effects  upon  the 
body.     Of  the  four,  coffee  has  the  greatest  amount  of  alkaloid 
and  its  use  in  excess  often  causes  wakefulness,  especially  in 
those  unaccustomed  to  its  use.     Cocoa  and  chocolate,  owing 
to  the  way  in  which  they  are  prepared  for  the  table,  have 
considerable  value  as  food.     Tea  and  coffee,  however,  are 
not  needed  by  growing  children  and  their  use  by  them  should 
be  discouraged.     Except  for  the  sugar  and  cream  they  con- 
tain, they  have  no  food  value.     In  adults,  however,  they  serve 
to  stimulate  the  flow  of  the  digestive  juices  and  by  their  flavors 
may  make  the  food  more  palatable. 

251.  Tobacco. — The   effect   of   the  alkaloid  in  tobacco  is 
secured  through  smoking  or  chewing  it,  or  using  the  powdered 
tobacco  as  snuff.     Various  other  plants  have  been  used  for 


THE   EFFECT   OF   DRUGS   ON   THE  BODY  293 

smoking,  but  tobacco  is  the  favorite  wherever  it  can  be  ob- 
tained. The  effects  of  tobacco,  however,  are  of  a  more  serious 
nature  than  those  produced  by  the  beverages.  The  alkaloid, 
nicotine,  which  it  contains,  is  deadly  poisonous  in  very  small 
quantities.  The  use  of  tobacco  diminishes  the  irritability  of 
the  cells  and  therefore  produces  disorder  in  practically  all  the 
tissues  of  the  body.  It  has  an  especially  injurious  effect  upon 
the  action  of  the  heart.  It  also  retards  the  growth  of  new  cells 
and  its  use  in  youth  often  results  in  a  stunting  of  bodily  growth. 
Its  effects  upon  the  nervous  system  may  be  seen  in  the  tremb- 
ling hand  and  unsteady  gait  of  the  tobacco  user.  In  adult 
life,  tobacco  may  possibly  be  indulged  in  with  little  harm,  but 
even  then,  it  is  an  expensive  luxury  which  once  taken  up  forms 
a  habit  that  often  inconveniences  its  votaries.  So  well  known 
are  the  effects  of  tobacco  upon  children  that  many  States 
forbid  its  sale  to  minors.  Cigarettes  appear  to  be  no  more 
harmful  than  cigars  except  for  the  fact  that  their  small  size 
and  cheapness  make  them  more  easily  accessible  to  the  begin- 
ner. Boys  who  are  learning  to  smoke  should  understand 
that  many  employers  discriminate  against  the  cigarette 
smoker  and  often  refuse  to  employ  him  at  any  price.  This 
fact,  alone,  should  be  sufficient  to  cause  those  who  hope  to  rise 
in  the  world  to  abstain  from  tobacco.  Those  who  use  tobacco 
are  nearly  always  slower  mentally  than  those  who  do  not  use  it. 
252.  Alcohol. — Unlike  other  drugs,  alcohol  is  not  derived 
from  any  particular  plant,  although  it  is  a  plant  product.  It 
is  formed  by  the  activities  of  yeast  on  sugary  solutions  whereby 
the  sugar  is  broken  up  into  carbon  dioxide  and  alcohol. 
When  taken  into  the  system  in  small  quantities,  alcohol  is 
oxidized  like  other  foods,  but  in  larger  amounts,  it  acts  as  a 
narcotic  whose  effects  are  especially  felt  in  the  nerves  which 
control  the  arteries  and  capillaries.  When  first  taken,  it  may 
produce  a  sensation  of  warmth  and  pleasant  lightness  of  feel- 
ing, but  its  effects  are  soon  felt  in  the  brain  which  it  may 
stupefy  to  such  an  extent  as  to  render  its  victim  insensible. 


294  EXPERIMENTAL   GENERAL   SCIENCE 

Owing  to  the  fact  that  it  is  a  habit  forming  drug,  the  moderate 
drinker  little  by  little  becomes  more  intemperate  until  he 
ends  a  mental  and  physical  wreck.  Many  States  now  forbid 
the  sale  within  their  borders  of  alcohol  for  drinking  and  in 
other  States  large  areas  have  become  "dry"  territory.  It 
will  probably  be  only  a  short  time  before  the  drinking  of 
alcohol  will  be  entirely  abolished.  One  of  the  most  forceful 
reasons  for  the  total  abstinence  from  alcohol  is  the  fact  that 
practically  all  positions  of  responsibility  are  now  barred  to  the 
user  of  strong  drink.  The  boy  who  begins  life  by  indulging  in 
beer,  wines,  whiskey,  and  other  liquors  starts  with  a  handicap 
which  he  can  scarcely  hope  to  overcome.  He  voluntarily 
undertakes  to  accept  menial  positions  with  small  chance  of 
attaining  the  good  salaries  and  easy  positions  of  his  fellows 
who  do  not  drink.  After  careful  investigation,  the  life  in- 
surance companies  have  discovered  that  the  average  length  of 
life  of  even  the  moderate  drinker  is  less  than  that  of  the  ab- 
stainer. This  is  partly  due  to  the  degeneration  which  alcohol 
causes  in  the  tissues,  and  partly  because  the  drinking  of  alcohol 
so  lowers  the  vitality  that  the  body  repels  disease  with  diffi- 
culty. Whenever  an  epidemic  of  disease  spreads  through  a 
locality,  it  is  the  drinking  man  who  first  succumbs  to  it. 

253.  Patent  Medicines. — The  shelves  of  every  drug  store 
are  stocked  with  a  vast  array  of  patent  medicines  which  mutely 
testify  to  the  widespread  habit  our  people  have  of  dosing 
themselves.  The  labels  on  the  bottles  usually  indicate  that 
the  contents  will  cure  a  variety  of  diseases,  though  the  regular 
physician  finds  it  necessary  to  prescribe  separately  for  each 
case.  There  may  be  some  patent  medicines  that  are  valuable, 
but  the  majority  owe  their  reputed  curative  powers  to  the 
effects  of  the  alcohol  which  they  contain.  In  several,  the 
percentage  of  alcohol  is  higher  than  it  is  in  whiskey.  Money 
paid  for  patent  medicines  is  usually  wasted.  It  is  a  good  rule 
to  take  no  medicine  of  any  kind  except  upon  the  advice  of  a 
physician. 


INDEX 


Absorption,  260 
Acclimatization,  220 
Acid  salt,  146 
Acids  in  plants,  145 

mineral,  145 

nature  of,  145 

neutralizing,  146 

test  for,  145 
Action,  involuntary,  246 

reflex,  247 

Affinity,  chemical,  29 
Air,  composition  of,  119 

function  of  constituents,  120 

pressure  of,  120 

vibrations  in,  167 

weight  of,  119 
Albino,  276 
Alcohol,  293 

Alimentary  canal,  structure  of,  253 
Alkalies,  146 
Alkaloids,  291 
Amalgams,  134 
Amorphous,  15 
Amphibians,  221 
Amylopsin,  255 
Anchor  ice,  63 
Annuals,  221 
Anticyclones,  97 
Antiseptics,  233 
Antitoxins,  232 
Appendicitis,  254 
Appendix,  254 


Armature,  208 
Arteries,  260 
Arthropoda,  221 
Astronomy,  2 
Atoms,  24 

Auricles  of  heart,  263 
Aurora  borealis,  203 
Autoclave,  68 
Autumn,  11 


Bacteria,  nature  of,  231 

work  of,  232 
Barograph,  123 
Barometer,  121 

aneroid,  122 
Barrier,  220 
Bases,  nature  of,  145 

tests  for,  145 
Bathing,  278 
Beverages,  292 
Big  dipper,  7 
Bile,  255 
Biology,  2 
Bleeding,  265 
Blisters,  276 
Blood,  259 

circulation,  263 

corpuscles,  red,  259 
white,  260 

stream,  regulation  of,  265 
Boiling,  47,  102 

affected  by  pressure,  66,  202 


295 


296 


INDEX 


Boiling  points,  table  of,  61 
Bones,  oroken,  242 

long  239 
Botany,  2 
Brain,  245 
Brass,  133 
Breast  bone, "239 
Breathing,  270 

organs  of,  268 

Breeding,  plant  and  animal,  229 
Bronchi,  269 
Bronze,  133 
Bunsen  burner,  77 
Buoyancy,  42 
Bureau  of  standards,  36 
Burning  glass,  152 


Calcium  light,  73 
Calorie,  69 
Camera,  153 
Capillaries,  260 
Capillarity,  114 

absorption  by,  114 
Carbohydrates,  214,  250 
Carbon  dioxide,  nature  of,  76 

preparing,  75 

test  for,  76,  77 

use  of,  76 
Carpels,  216 
Cartilage,  240 
Casting,  56 
Catalyzers,  28 
Cell  sap,  212 
CeUs,  living,  211 
Centigrade  degrees,  49 
Centrifugal  force,  174 
Centripetal  force,  174 
Cerebellum,  246 
Cerebrum,  246 


Change,  chemical,  16 

in  nature,  224 

of  state,  62 

physical,  16 
Charged  bodies,  200 
Chemical  change,  heat  and,  30 

elements,  table  of,  26 
Chemistry,  2 
Chloroplasts,  213 
Cloud,  109 

forms,  110 
Cohesion,  54 
Colds,  272 
Color,  absorption  of,  162 

blind,  164 

eye  and,  164 

reflection  of,  162 
Colors,  complimentary,  163 

prismatic,  160 
Combustion,  products  of,  74 

spontaneous,  74 
Comets,  10 
Compass,  195 

Compounds,  chemical,  24,  27 
Condensation,  106 

forms  of,  109 
Condensers,  202 
Conduction,  83 
Conductors  of  electricity,  202 

of  heat,  84 
Congestion,  265 
Connective  tissue,  240 
Consciousness,  284 
Constellations,  7 

motion  of,  7 
Convection  and  frost,  98 

circuits,  95 

currents,  95 

in  liquids,  97 

Cooling  by  evaporation,  103 
Cranium,  239 


INDEX 


297 


Crystallization,  131 

water  of,  133 
Crystals,  15,  131 
Cuticle,  275 
Cyclones,  96 

D 

Darwinian  theory,  255 
Day,  11 
Degrees,  182 
Deliquescence,  114 
Densities,  table  of,  43 
Density,  measuring,  39 
Dermis,  275,  276 
Dew,  109 
Dewpoint,  106 
Diaphragm,  241 
Diffusion,  132 
Digestion,  215,  250 
Digestive  juices,  254 

system,  253 
Diminishing  glass,  153 
Dioecious  plants,  217 
Dip-needle,  196 
Disinfectants,  233 
Distillate,  141 
Distillation,  140 

destructive,  142 

fractional,  142 

Distribution  of  living  things,  220 
Drugs,  291 

habit-forming,  292 
Dusting,  271 
Dyes  from  coal  tar,  142 

E 

Earth,  distances  on,  182 

time  on,  182 
Earthshine,  10 


Echoes,  168 
Eclipses,  10 
Efflorescence,  115 
Eggs,  216 
Elasticity,  15 
Electric  bells,  208 

cranes,  208 

current,  direction  of,  206 

currents,  induced,  206 

generator,  209 

light,  209 
Electricity,  frictional,  199 

positive,  200 

static,  199 

Electrified  bodies,  200 
Electrifying  by  induction,  201 
Electrodes,  206 
Electrolysis,  207 
Electrolyte,  206 
Electro-magnets,  207 
Electroplating,  207 
Electroscope,  201 
Electrotyping,  207 
Elements,  chemical,  24 

distribution  of,  25 
Emulsions,  134 
Energy,  chemical,  19 

electrical,  19  . 

forms  of,  19 

heat,  20 

kinetic,  21 

matter  distinguished  from,  13 

potential,  21 

radiant,  21 

sources  of,  21 

Engine,  internal  combustion,  70 
Engines,  gas,  70 
Enzymes,  215,  250 
Epidermis,  275 
Epiglottis,  270 
Equator,  181 


298 


INDEX 


Equilibrium,  176 

sense,  285 
Equinoxes,  184 
Esophagus,  269 
Evaporation  55,  101 

conditions  affecting,  101 

effects  of,  103 
Evolution,  223 

organic,  225 
Excretion,  280 

conditions  affecting,  282 
Exercise,  241 
Explosions,  74 
Eye  and  color,  164 


Fahrenheit  degrees,  49 

Families,  plant  and  animal,  218 

Fauna,  220 

Fever,  278 

Filters,  139 

Fire  extinguishers,  77 

Fireless  cooker,  88 

Flocculation,  139 

Flora,  220 

Flower,  216 

Fluids,  19 

Fluorescence,  162 

Fluoroscope,  163 

Focus,  152 

Fog,  109 

Food,  250 

making,  213 

values,  251 

Formulas,  chemical,  26 
Fossils,  223 
Freckles,  276 
Freezing,  47 
Friction,  174 

effect  of  oil  on,  175 


Friction,  rolling,  174 

sliding,  174 
Frost,  109 

convection  and,  198 

effect  of,  57 
Fulcrum,  189 


Gall  bladder,  255 

Gametes,  216 

Gas,  effect  of  heat  on,  19 

engine,  70 
Gases,  14 

and  vapors,  103 

colors  of,  103 

compression  of,  67 

cooled  by  expansion,  68 

effect  of  compression  on,  67 

expansion  of,  55 
Gastric  juice,  255 
Genera,  218 
Geology,  2 
Glands,  215 

of  the  skin,  277 

sebaceous,  277 

sweat,  277 

tear,  288 

Globe,  locating  points  on,  181 
Glycogen,  261 
Gooseflesh,  277 
Grams,  35 
Gravity,  175 

center  of,  176 

specific,  40 
Growth,  213 
Gulf  stream,  298 


Habitats,  225 
Haemoglobin,  261 


INDEX 


299 


Hail,  209 

Hair  follicles,  246 

structure  of,  277 
Hearing,  285,  286 
Heart,  260,  262,  263 

beat,  262 
Heat  affected  by  latitude,  86 

and  direction  of  sun's  rays,  86 

and  electricity,  209 

and  living  things,  87 

and  respiration,  88 

distribution  of,  85 

latent,  62 

of  fusion,  63 

of  vaporization,  63 

specific,  69 

transference  of,  83 
Hiccough,  273 
Hot-water  heating,  98 
Humidity,  107 

absolute,  107 

relative,  107 
Hybridizing,  229 
Hydrometer,  41 
Hygrometer,  108 


Ice-cream  freezer,  88 
Images,  persistence  of,  154 
Inertia,  173 
Inorganic  bodies,  211 
Insulators  of  electricity,  202 

of  heat,  84 
Intestines,  253 
Invar,  57 
Invertebrates,  221 
Iris,  287 

J 

Japan  current,  98 
Joints,  239 


K 

Kidneys,  280 
Kilocalorie,  69,  252 


Lacteals,  261 

Lantern,  projection,  153 

Larynx,  269 

Latent  heats,  table  of,  63 

Latitude,  181 

Lens,  crystalline,  287 

Lenses,  152 

double  concave,  152 

convex,  162 
Levers,  189 
Ley  den  jar,  202 
Lianes,  221 
Ligaments,  240 
Light,  149 

and  phosphorescence,  155 

composition  of,  160 

effect  of  prism  upon,  161 

effects  of,  154 

energy  used  by  plants,  155 

rays,  direction  of,  149 
infra-red,  162 
ultra-violet,  162 

reflection  of,  150 

speed  of,  22,  149 

vibrations  of,  22 

white,  160,  163 
Lighting,  artificial,  156 

indirect,  156 
Lightning,  heat,  203 
Lines  of  force,  196 
Liquids,  14 

convection  in,  97 

free  surface  of,  15 
Liver,  255 
Lodestone,  194 


300 


INDEX 


Longitude,  181 
Luminous  bodies,  149 
Lymph,  261 

M 

Machines,    mechanical  advantage 
of,  188 

perpetual  motion,  188 

pole,  195 

simple,  188 
Magnetoscope,  195 
Magnetism,  194 
Magnetizing  by  induction,  197 
Magnet,  poles  of,  195 
Magnets,  artificial,  194 

bar,  194 

horseshoe,  194 

natural,  194 
Magnifying  glass,  153 
Mass,  39 

Matter  distinguished  from  energy, 
13 

indestructible,  16 

movements  of,  18 

properties  of,  15 
Medulla  oblongata,  246 
Megaphone,  168 
Melting  point,  54 

points,  table  of,  61 
Mendel's  law,  229 
Meridians,  181 
Metals,  fusible,  133 
Meteorites,  10 
Meter,  34 

cubic,  36 

divisions  of,  35 
Metric  system,  33 

advantages  of,  34 

ton,  36 
Microscope,  153 


Milky  way,  5 

Moisture  in  the  air,  106,  119 

Molecular  motion,  18 

theory,  13 
Molecules,  13 

speed  of,  18 
Mollusca,  221 
Momentum,  173 
Monoecious  plants,  218 
Month,  11 
Moon,  9 

full,  10 

new,  10 
Mulch,  89 
Muscles,  240 
Mutants,  228 
Mutation  theory,  227 

N 

Names,  scientific,  219 

vernacular,  219 
Natural  selection,  227 
Nerves,  245 
Night,  11 
Noon,  182 
Northern  lights,  203 
Nucleus  of  cell,  212 


Occlusion,  133 
Opaque  bodies,  16 
Orders,  218 
Organic  bodies,  211 

kingdom,  213 
Organs,  212 
Osmosis,  115 

Oxidation,  heat  and  light  from,  72 
Oxygen,  activity  of,  72 

need  of,  271 

preparing,  75 


INDEX 


301 


Pain,  247 

Paint,  luminous,  155 
Pancreatic  juice,  255 
Papillse,  276 
Parallels,  181 
Parasites,  231 
Patent  medicines,  294 
Pendulum,  compensated,  57 
Pepsin,  254 
Peptones,  254 
Perennials,  221 
Perspiration,  function  of,  277 
Petals,  217 
Phosphorescence,  155 
Photosynthesis,  214 
Physics,  2 
Physiography,  2 
Physiology,  2 
Plane,  inclined,  190 
Planets,  8,  9 

orbits  of,  9 

Plant  and  animal  breeding,  229 
Plasma,  259 
Plumb  bob,  176 
Pole,  negative,  206 

positive,  206 

star,  6,  8 

Poles  of  a  battery,  206 
Pollen  grains,  216 
Pollination,  217 
Precipitates,  139 
Preservatives,  234 
Press,  hydraulic,  190 
Pressure  cooker,  68 

uses  of,  69 
Primary  colors,  160 
Proteins,  214 
Protoplasm,  211 
Psychrometer,  108 


Ptomaines,  232 
Ptyalin,  254 
Pump,  force,  124 
lift,  123 

R 

Radiation,  84 

affected  by  color,  85 

effect  of  dust  on,  87 

of  gases  on,  87 
Rainbow,  161 
Range  of  living  things,  220 
Reflection,  angle  of,  151 
Reflectors  of  heat,  85 

of  light,  150 
Refrigeration,  68 

gases  used  in,  69 
Reproduction,  216 
Resonance,  169 
Respiration,  215,  268 

and  heat,  88 
Reverberations,  169 
Roentgen  rays,  163 
Round  shoulders,  242 


Saliva,  254 
Salt,  acid,  146 

basic,  146 
Salts,  146 

formation  of,  146 
Saprophytes,  231 
Saturation  point,  106 
Science,  applied,  2 

definition  of,  1 

pure,  2 

special,  2 

Scientific  names,  219 
Seasons,  11,  184 
Sensations,  284 

general,  284 


302 


INDEX 


Sense,  special  end  organs  of,  285 

Senses,  special,  285 

Sepals,  217 

Serums,  233 

Shrinking,  115 

Shrubs,  221 

Sighing,  273 

Sight,  285,  286 

Silver,  German,  133 

Simmering,  102 

Siphon,  124 

Skeleton,  arrangement  of,  237 

use  of,  237 
Skin,  275 
Skull,  239 
Sleep,  248 
Smell,  285 
Snoring,  273 
Snow,  109 
Soaps,  146 
Solar  system,  8 
Solids,  14 

change  in  volume  of,  55 
Solstices,  184 
Solutes,  129 

Solution,  conditions  affecting,  130 
Solutions,  129,  130 

and  change  of  state,  134 

dilute,  130 

strength  of,  130 

supersaturated,  131 
Solvents,  129 
Sound,  167 

speed  of,  167 
Sounding  board,  168 
Sounds,  distinguishing,  169 
Species,  218 

elementary,  238 
Specific  gravity  bottle,  41 

heat,  61 

heats,  table  of,  61 


Spectroscope,  161 
Spectrum,  161 

solar,  161 
Sperms,  216 
Sphincters,  241 
Spinal  cord,  245,  246 
Spine,  237 
Spirit  level,  43 
Spores,  216 
Sports,  228 
Sprains,  242 
Spring,  11 
Stamens,  216 
Stars,  5 

fixed,  8 

light  of,  6 

shooting,  10 
Steapsin,  255 
Stereopticon,  153 
Sterilizing,  234 
Stomach,  253 
Storage  batteries,  210 
Struggle  for  existence,  226 
Sublimation,  55,  101 
Summer,  11 
Sun,  8 

time,  182 
Sutures,  239 
Sweetbreads,  255 
Symbols,  chemical,  26 


Tan,  276 

Taste,  285 

Teeth,  255 

Telescope,  153 

Temperature,  kindling,  73 
lag  in,  86 

measurement  of,  46 
sense,  46,  88,  285 

Tendons,  240 


INDEX 


303 


Thermograph,  51 
Thermometer,  Centigrade,  47 

clock,  50 

Fahrenheit,  47 

maximum,  51 

minimum,  51 

scales,  47 

Thermometers,  other,  56 
Thermos  bottle,  89 
Thermostat,  51 
Thoracic  duct,  261 
Tides,  175 
Time  belts,  182 

on  the  earth,  11 

standard,  183 

sun,  182 
Tinctures,  129 
Tissue,  connective,  240 
Tissues,  212 
Tobacco,  292 
Touch,  285 
Toxins,  232 
Trachea,  268 
Transformers,  207 
Trees,  221 
Tropics,  184 
Turbines,  70 
Type  metal,  133 


Veins,  260 
Ventilation,  271 
Ventricle,  263 
Vernier,  121 
Vertebrae,  237 
Vertebrates,  221 
Vibrations,  forced,  169 

sympathetic,  169 
Voice,  272 
Volatile  liquids,  101 
Voltaic  cell,  205 

W 

Warping,  115 
Warts,  276 
Water,  alkali,  131 

an  aid  to  weathering,  224 

hard,  132 

level,  113 

mineral,  131 

of  crystallization,  133 

softening,  132 

specific  heat  of,  61 

vapor  in  saturated  air,  107 
Weight,  39 

Welsbach  gas  light,  73 
Wind,  95 
Winter,  11 


U 

Universe,  extent  of,  5 
Ureter,  282 


X-rays,  163 


Yawning,  273 
Year,  11 


Vacuoles,  212 
Vacuum,  13 
Vapors,  gases  and,  103 
Variation  in  nature,  225 
Varieties,  228 


Zero,  47 

absolute,  48 
Zones,  183 
Zoology,  2 


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